Cisco Applied Mitigation Bulletin-
Cisco Response
This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Cisco Unified Communications Manager IM and Presence Service Denial of Service Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
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The Cisco Unified IM and Presence Service exhibits a vulnerability when processing a flood of TCP IP version 4 (IPv4) and IP version 6 (IPv6) packets. This vulnerability can be exploited remotely without authentication. Successful exploitation of this vulnerability could result in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition.
The attack vectors for exploitation are through IPv4 and IPv6 packets using the following protocols and ports:
- TCP port 5060
- TCP port 5061
An attacker could exploit this vulnerability using spoofed packets.
This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2013-3453.
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Information about vulnerable, unaffected, and fixed software is available in the Cisco Security Advisory, which is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20130821-cup
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Cisco devices provide several countermeasures for this vulnerability. Administrators are advised to consider these protection methods to be general security best practices for infrastructure devices and the traffic that transits the network. This section of the document provides an overview of these techniques.
Cisco IOS Software can provide effective means of exploit prevention using the following methods:
- Transit access control lists (tACLs)
- Unicast Reverse Path Forwarding (uRPF)
- IP source guard (IPSG)
These protection mechanisms filter and drop, as well as verify the source IP address of, packets that are attempting to exploit this vulnerability.
The proper deployment and configuration of uRPF provides an effective means of protection against attacks that use packets with spoofed source IP addresses. uRPF should be deployed as close to all traffic sources as possible.
The proper deployment and configuration of IPSG provides an effective means of protection against spoofing attacks at the access layer.
Effective means of exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance, Cisco Catalyst 6500 Series ASA Services Module (ASASM), and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers using the following:
- tACLs
- Threat Detection
- Connection Limits
- uRPF
These protection mechanisms filter and drop, as well as verify the source IP address of, packets that are attempting to exploit this vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.
Cisco IOS Software, Cisco ASA, Cisco ASASM, Cisco FWSM firewalls, and Cisco ACE Application Control Engine Appliance and Module can provide visibility through syslog messages and counter values displayed in the output from show commands.
The Cisco Security Manager can also provide visibility through incidents, queries, and event reporting.
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Organizations are advised to follow their standard risk evaluation and mitigation processes to determine the potential impact of this vulnerability. Triage refers to sorting projects and prioritizing efforts that are most likely to be successful. Cisco has provided documents that can help organizations develop a risk-based triage capability for their information security teams. Risk Triage for Security Vulnerability Announcements and Risk Triage and Prototyping can help organizations develop repeatable security evaluation and response processes.
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Caution:The effectiveness of any mitigation technique depends on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. As with any configuration change, evaluate the impact of this configuration prior to applying the change.
Specific information about mitigation and identification is available for these devices:
- Cisco IOS Routers and Switches
- Cisco IOS NetFlow and Cisco IOS Flexible NetFlow
- Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls
- Cisco Security Manager
Cisco IOS Routers and Switches
Mitigation: Transit Access Control Lists
To protect the network from traffic that enters the network at ingress access points, which may include Internet connection points, partner and supplier connection points, or VPN connection points, administrators are advised to deploy transit access control lists (tACLs) to perform policy enforcement. Administrators can construct a tACL by explicitly permitting only authorized traffic to enter the network at ingress access points or permitting authorized traffic to transit the network in accordance with existing security policies and configurations. A tACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The tACL policy denies unauthorized IPv4 and IPv6 packets on TCP port 5060 and 5061 that are sent to affected devices. In the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP address space that is used by the affected devices, and the hosts at 192.168.100.1 and 2001:DB8::100:1 are considered trusted sources that require access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.
Additional information about tACLs is in Transit Access Control Lists: Filtering at Your Edge.
! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable TCP ports and protocol ! access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Explicit deny for all other IP traffic ! access-list 150 deny ip any any ! !-- Create the corresponding IPv6 tACL ! ipv6 access-list IPv6-Transit-ACL-Policy ! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable << TCP ports and protocols> ! permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060 permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5061 ! !-- The following vulnerability-specific ACEs can !-- aid in identification of attacks to global and !-- link-local addresses ! deny tcp any 2001:DB8:1:60::/64 eq 5060 deny tcp any 2001:DB8:1:60::/64 eq 5061 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in !-- accordance with existing security policies and configurations !-- and allow IPv6 neighbor discovery packets, which !-- include neighbor solicitation packets and neighbor !-- advertisement packets ! permit icmp any any nd-ns permit icmp any any nd-na !
!-- Explicit deny for all other IPv6 traffic !
deny ipv6 any any ! ! !-- Apply tACLs to interfaces in the ingress direction ! interface GigabitEthernet0/0 ip access-group 150 in ipv6 traffic-filter IPv6-Transit-ACL-Policy inNote that filtering with an interface access list will elicit the transmission of ICMP unreachable messages back to the source of the filtered traffic. Generating these messages could have the undesired effect of increasing CPU utilization on the device. In Cisco IOS Software, ICMP unreachable generation is limited to one packet every 500 milliseconds by default. ICMP unreachable message generation can be disabled using the interface configuration commands no ip unreachables and no ipv6 unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration commands ip icmp rate-limit unreachable interval-in-ms and ipv6 icmp error-interval interval-in-ms.
Identification: Transit Access Control Lists
After the administrator applies the tACL to an interface, show ip access-lists and show ipv6 access-list commands will identify the number of IPv4 and IPv6 packets on tcp port 5060 and 5061 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit this vulnerability. Example output for show ip access-lists 150 and show ipv6 access-list IPv6-Transit-ACL-Policy follows:
router#show ip access-lists 150 Extended IP access list 150 10 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 30 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 (12 matches) 40 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 (26 matches) 50 deny ip any any router#In the preceding example, access list 150 has dropped the following packets received from an untrusted host or network:
- 12 packets on TCP port 5060 for ACE line 30
- 26 packets on TCP port 5061 for ACE line 40
router#show ipv6 access-list IPv6-Transit-ACL-Policy IPv6 access list IPv6-Transit-ACL-Policy permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060 (55 matches) sequence 10 permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5061 (38 matches) sequence 20 deny tcp any 2001:DB8:1:60::/64 eq 5060 (30 matches) sequence 30 deny tcp any 2001:DB8:1:60::/64 eq 5061 (41 matches) sequence 40 permit icmp any any nd-ns (41 matches) sequence 50 permit icmp any any nd-na (41 matches) sequence 60 deny ipv6 any any (21 matches) sequence 70In the preceding example, access list IPv6-Transit-ACL-Policy has dropped the following packets received from an untrusted host or network:
- 30 packets on tcp port 5060 for ACE line 30
- 41 packets on tcp port 5061 for ACE line 40
For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Cisco Security Intelligence Operations white paper.
Administrators can use Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Cisco Security Intelligence Operations white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.
Identification: Access List Logging
The log and log-input access control list (ACL) option will cause packets that match specific ACEs to be logged. The log-input option enables logging of the ingress interface in addition to the packet source and destination IP addresses and ports.
Caution: Access control list logging can be very CPU intensive and must be used with extreme caution. Factors that drive the CPU impact of ACL logging are log generation, log transmission, and process switching to forward packets that match log-enabled ACEs.
For Cisco IOS Software, the ip access-list logging interval interval-in-ms command can limit the effects of process switching induced by IPv4 ACL logging. The logging rate-limit rate-per-second [except loglevel] command limits the impact of log generation and transmission.
The CPU impact from ACL logging can be addressed in hardware on the Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers with Supervisor Engine 720 or Supervisor Engine 32 using optimized ACL logging.
For additional information about the configuration and use of ACL logging, reference the Understanding Access Control List Logging Cisco Security white paper.
Mitigation: Spoofing Protection
Unicast Reverse Path Forwarding
The vulnerabilities that are described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure Unicast Reverse Path Forwarding (uRPF) as a protection mechanism against spoofing.
uRPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on uRPF to provide complete spoofing protection because spoofed packets may enter the network through a uRPF-enabled interface if an appropriate return route to the source IP address exists. Administrators are advised to take care to ensure that the appropriate uRPF mode (loose or strict) is configured during the deployment of this feature because it can drop legitimate traffic that is transiting the network. In an enterprise environment, uRPF may be enabled at the Internet edge and the internal access layer on the user-supporting Layer 3 interfaces.
For additional information about the configuration and use of uRPF, reference the Understanding Unicast Reverse Path Forwarding Cisco Security white paper.
IP Source Guard
IP source guard (IPSG) is a security feature that restricts IP traffic on nonrouted, Layer 2 interfaces by filtering packets based on the DHCP snooping binding database and manually configured IP source bindings. Administrators can use IPSG to prevent attacks from an attacker who attempts to spoof packets by forging the source IP address and/or the MAC address. When properly deployed and configured, IPSG coupled with strict mode uRPF provides the most effective means of spoofing protection for the vulnerabilities that are described in this document.
Additional information about the deployment and configuration of IPSG is in Configuring DHCP Features and IP Source Guard.
Identification: Spoofing Protection Using Unicast Reverse Path Forwarding
With uRPF properly deployed and configured throughout the network infrastructure, administrators can use the show cef interface type slot/port internal, show ip interface, show cef drop, show ip cef switching statistics feature, and show ip traffic commands to identify the number of packets that uRPF has dropped.
Note: Beginning with Cisco IOS Software Release 12.4(20)T, the command show ip cef switching has been replaced by show ip cef switching statistics feature.
Note: The show command begin regex and show command include regex command modifiers are used in the following examples to minimize the amount of output that administrators will need to parse to view the desired information. Additional information about command modifiers is in the show command sections of the Cisco IOS Configuration Fundamentals Command Reference.
router#show cef interface GigabitEthernet 0/0 internal | include drop ip verify: via=rx (allow default), acl=0, drop=18, sdrop=0 IPv6 unicast RPF: via=rx acl=None, drop=10, sdrop=0 (if IPv6 applies) router#
Note: show cef interface type slot/port internal is a hidden command that must be fully entered at the command-line interface. Command completion is not available for it.
router#show cef drop CEF Drop Statistics Slot Encap_fail Unresolved Unsupported No_route No_adj ChkSum_Err RP 27 0 0 18 0 0 router# router#show ip interface GigabitEthernet 0/0 | begin verify IP verify source reachable-via RX, allow default, allow self-ping 18 verification drops 0 suppressed verification drops router# router#show ipv6 interface GigabitEthernet 0/0 | section IPv6 verify IPv6 verify source reachable-via rx 0 verification drop(s) (process), 10 (CEF) 0 suppressed verification drop(s) (process), 0 (CEF) -- CLI Output Truncated -- router# router#show ip cef switching statistics feature IPv4 CEF input features:
Path Feature Drop Consume Punt Punt2Host Gave route
RP PAS uRPF 18 0 0 0 0 Total 18 0 0 0 0 -- CLI Output Truncated -- router# router#show ipv6 cef switching statistics feature IPv6 CEF input features: Feature Drop Consume Punt Punt2Host Gave route RP LES Verify Unicast R 10 0 0 0 0 Total 10 0 0 0 0 -- CLI Output Truncated -- router# router#show ip traffic | include RPF 18 no route, 18 unicast RPF, 0 forced drop router# router#show ipv6 traffic | include RPF 10 RPF drops, 0 RPF suppressed, 0 forced drop router#In the preceding show cef interface type slot/port internal, show cef drop, show ip interface type slot/port and show ipv6 interface type slot/port, show ip cef switching statistics feature and show ipv6 cef switching statistics feature, and show ip traffic and show ipv6 traffic examples, uRPF has dropped the following packets received globally on all interfaces with uRPF configured because of the inability to verify the source address of the IP packets within the forwarding information base of Cisco Express Forwarding.
- 18 IPv4 packets
- 10 IPv6 packets
Cisco IOS NetFlow and Cisco IOS Flexible NetFlow
Identification: IPv4 Traffic Flow Identification Using Cisco IOS NetFlow
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of IPv4 traffic flows that may be attempts to exploit this vulnerability. Administrators are advised to investigate flows to determine whether they are attempts to exploit this vulnerability or whether they are legitimate traffic flows.
router#show ip cache flow IP packet size distribution (90784136 total packets): 1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480 .000 .698 .011 .001 .004 .005 .000 .004 .000 .000 .003 .000 .000 .000 .000 512 544 576 1024 1536 2048 2560 3072 3584 4096 4608 .000 .001 .256 .000 .010 .000 .000 .000 .000 .000 .000 IP Flow Switching Cache, 4456704 bytes 1885 active, 63651 inactive, 59960004 added 129803821 ager polls, 0 flow alloc failures Active flows timeout in 30 minutes Inactive flows timeout in 15 seconds IP Sub Flow Cache, 402056 bytes 0 active, 16384 inactive, 0 added, 0 added to flow 0 alloc failures, 0 force free 1 chunk, 1 chunk added last clearing of statistics never Protocol Total Flows Packets Bytes Packets Active(Sec) Idle(Sec) -------- Flows /Sec /Flow /Pkt /Sec /Flow /Flow TCP-Telnet 11393421 2.8 1 48 3.1 0.0 1.4 TCP-FTP 236 0.0 12 66 0.0 1.8 4.8 TCP-FTPD 21 0.0 13726 1294 0.0 18.4 4.1 TCP-WWW 22282 0.0 21 1020 0.1 4.1 7.3 TCP-X 719 0.0 1 40 0.0 0.0 1.3 TCP-BGP 1 0.0 1 40 0.0 0.0 15.0 TCP-Frag 70399 0.0 1 688 0.0 0.0 22.7 TCP-other 47861004 11.8 1 211 18.9 0.0 1.3 UDP-DNS 582 0.0 4 73 0.0 3.4 15.4 UDP-NTP 287252 0.0 1 76 0.0 0.0 15.5 UDP-other 310347 0.0 2 230 0.1 0.6 15.9 ICMP 11674 0.0 3 61 0.0 19.8 15.5 IPv6INIP 15 0.0 1 1132 0.0 0.0 15.4 GRE 4 0.0 1 48 0.0 0.0 15.3 Total: 59957957 14.8 1 196 22.5 0.0 1.5 SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 06 0984 13C4 1 Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 06 0911 13C4 3 Gi0/1 192.168.150.60 Gi0/0 10.89.16.226 06 0016 12CA 1 Gi0/0 192.168.13.97 Gi0/1 192.168.60.28 06 0B3E 13C5 5 Gi0/0 192.168.10.17 Gi0/1 192.168.60.97 06 0B89 13C5 1 Gi0/0 10.88.226.1 Gi0/1 192.168.202.22 11 007B 007B 1 Gi0/0 192.168.12.185 Gi0/1 192.168.60.239 11 0BD7 00A1 1 Gi0/0 10.89.16.226 Gi0/1 192.168.150.60 06 12CA 0016 1 router#In the preceding example, there are multiple flows on TCP port 5060 (hex value 13C4) and TCP port 5061 (hex value 13C5).
This traffic is sourced from and sent to addresses within the 192.168.60.0/24 address block, which is used by affected devices. The packets in these flows may be spoofed and may indicate an attempt to exploit this vulnerability. Administrators are advised to compare these flows to baseline utilization for traffic sent on tcp ports 5060 and 5061, and also investigate the flows to determine whether they are sourced from untrusted hosts or networks.
As shown in the following example, to view only the packets on TCP port 5060 (hex value 13C4) and TCP port 5061 (hex value 13C5), use the show ip cache flow | include SrcIf|_06_.*(13C4|13C4)_ command to display the related Cisco NetFlow records:
TCP Flowsrouter#show ip cache flow | include SrcIf|_06_.*(13C4|13C4)_ SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.12.110 Gi0/1 192.168.60.163 06 092A 13C4 6 Gi0/0 192.168.11.230 Gi0/1 192.168.60.20 06 0C09 13C4 1 Gi0/0 192.168.11.131 Gi0/1 192.168.60.245 06 0B66 13C4 18 Gi0/0 192.168.13.7 Gi0/1 192.168.60.162 06 0914 13C5 1 Gi0/0 192.168.41.86 Gi0/1 192.168.60.27 06 0B7B 13C5 2 router#
Identification: IPv6 Traffic Flow Identification Using Cisco IOS NetFlow
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of IPv6 traffic flows that may be attempts to exploit the vulnerabilities that are described in this document. Administrators are advised to investigate flows to determine whether they are attempts to exploit this vulnerability or whether they are legitimate traffic flows.
The following output is from a Cisco IOS device running Cisco IOS Software 12.4 mainline train. The command syntax will vary for different Cisco IOS Software trains.
router#show ipv6 flow cache IP packet size distribution (50078919 total packets): 1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480 .000 .990 .001 .008 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 512 544 576 1024 1536 2048 2560 3072 3584 4096 4608 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 IP Flow Switching Cache, 475168 bytes 8 active, 4088 inactive, 6160 added 1092984 ager polls, 0 flow alloc failures Active flows timeout in 30 minutes Inactive flows timeout in 15 seconds IP Sub Flow Cache, 33928 bytes 16 active, 1008 inactive, 12320 added, 6160 added to flow 0 alloc failures, 0 force free 1 chunk, 1 chunk added SrcAddress InpIf DstAddress OutIf Prot SrcPrt DstPrt Packets 2001:DB...06::201 Gi0/0 2001:DB...28::20 Local 0x06 0x16C4 0x13C4 1464 2001:DB...6A:5BA6 Gi0/0 2001:DB...28::21 Gi0/1 0x3A 0x0000 0x8000 1191 2001:DB...6A:5BA6 Gi0/0 2001:DB...134::3 Gi0/1 0x3A 0x0000 0x8000 1191 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::4 Gi0/1 0x3A 0x0000 0x8000 1192 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x13C4 1597 2001:DB...06::201 Gi0/0 2001:DB...128::3 Gi0/1 0x06 0x1610 0x13C5 1001 2001:DB...06::201 Gi0/0 2001:DB...128::4 Gi0/1 0x06 0x1634 0x13C4 1292 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::3 Gi0/1 0x3A 0x0000 0x8000 1155 2001:DB...6A:5BA6 Gi0/0 2001:DB...146::3 Gi0/1 0x3A 0x0000 0x8000 1092 2001:DB...6A:5BA6 Gi0/0 2001:DB...144::4 Gi0/1 0x3A 0x0000 0x8000 1193To permit display of the full 128-bit IPv6 address, use the terminal width 132 exec mode command.
In the preceding example, there are multiple IPv6 flows on TCP port 5060 (hex value 13C4) and TCP port 5061 (hex value 13C5).
As shown in the following example, to view only the packets on TCP port 5060 (hex value 13C4) and TCP port 5061 (hex value 13C5), use the show ipv6 flow cache | include SrcIf|_06_.*(13C4|13C5)_ command to display the related Cisco NetFlow records:
TCP Flows
router#show ipv6 flow cache | include SrcIf|_06_.*(13C4|13C5)_ SrcAddress InpIf DstAddress OutIf Prot SrcPrt DstPrt Packets 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x13C4 1597 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x13C5 1597 router#
Identification: IPv4 Traffic Flow Identification Using Cisco Flexible NetFlow
Introduced in Cisco IOS Software Releases 12.2(31)SB2 and 12.4(9)T, Cisco IOS Flexible NetFlow improves original Cisco NetFlow by adding the capability to customize the traffic analysis parameters for the administrator's specific requirements. Original Cisco NetFlow uses a fixed seven tuples of IP information to identify a flow, whereas Cisco IOS Flexible NetFlow allows the flow to be user defined. It facilitates the creation of more complex configurations for traffic analysis and data export by using reusable configuration components.
The following example output is from a Cisco IOS device that is running a version of Cisco IOS Software in the 15.1T train. Although the syntax will be almost identical for the 12.4T and 15.0 trains, it may vary slightly depending on the actual Cisco IOS release being used. In the following configuration, Cisco IOS Flexible NetFlow will collect information on interface GigabitEthernet0/0 for incoming IPv4 flows based on source IPv4 address, as defined by the match ipv4 source address key field statement. Cisco IOS Flexible NetFlow will also include nonkey field information about source and destination IPv4 addresses, protocol, ports (if present), ingress and egress interfaces, and packets per flow.
! !-- Configure key and nonkey fields !-- in the user-defined flow record ! flow record FLOW-RECORD-ipv4 match ipv4 source address collect ipv4 protocol collect ipv4 destination address collect transport source-port collect transport destination-port collect interface input collect interface output collect counter packets ! !-- Configure the flow monitor to !-- reference the user-defined flow !-- record ! flow monitor FLOW-MONITOR-ipv4 record FLOW-RECORD-ipv4 ! !-- Apply the flow monitor to the interface !-- in the ingress direction ! interface GigabitEthernet0/0 ip flow monitor FLOW-MONITOR-ipv4 input
The Cisco IOS Flexible NetFlow flow output is as follows:
router#show flow monitor FLOW-MONITOR-ipv4 cache format table Cache type: Normal Cache size: 4096 Current entries: 6 High Watermark: 1 Flows added: 9181 Flows aged: 9175 - Active timeout ( 1800 secs) 9000 - Inactive timeout ( 15 secs) 175 - Event aged 0 - Watermark aged 0 - Emergency aged 0 IPV4 SRC ADDR ipv4 dst addr trns src port trns dst port intf input intf output pkts ip prot =============== =============== ============= ============= ========== =========== ====== ======= 192.168.10.201 192.168.60.102 1456 5060 Gi0/0 Gi0/1 1128 6 192.168.11.54 192.168.60.158 123 5060 Gi0/0 Gi0/1 2212 6 192.168.150.60 10.89.16.226 2567 443 Gi0/0 Gi0/1 13 6 192.168.13.97 192.168.60.28 3451 5061 Gi0/0 Gi0/1 1 6 192.168.10.17 192.168.60.97 4231 5060 Gi0/0 Gi0/1 146 6 10.88.226.1 192.168.202.22 2678 443 Gi0/0 Gi0/1 10567 6 10.89.16.226 192.168.150.60 3562 80 Gi0/0 Gi0/1 30012 6To only view the packets on TCP port 5060 and 5061, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_(5060|5061)_.*_6_ command to display the related NetFlow records.
For more information about Cisco IOS Flexible NetFlow, refer to Flexible Netflow Configuration Guide, Cisco IOS Release 15M&T and Cisco IOS Flexible NetFlow Configuration Guide, Release 12.4T.
Identification: IPv6 Traffic Flow Identification Using Cisco IOS Flexible NetFlow
The following example output is from a Cisco IOS device that is running a version of Cisco IOS Software in the 15.1T train. Although the syntax will be almost identical for the 12.4T and 15.0 trains, it may vary slightly depending on the actual Cisco IOS release being used. In the following configuration, Cisco IOS Flexible NetFlow will collect information on interface GigabitEthernet0/0 for incoming IPv6 flows based on the source IPv6 address, as defined by the match ipv6 source address key field statement. Cisco IOS Flexible NetFlow will also include nonkey field information about source and destination IPv6 addresses, protocol, ports (if present), ingress and egress interfaces, and packets per flow.! !-- Configure key and nonkey fields !-- in the user-defined flow record ! flow record FLOW-RECORD-ipv6 match ipv6 source address collect ipv6 protocol collect ipv6 destination address collect transport source-port collect transport destination-port collect interface input collect interface output collect counter packets ! !-- Configure the flow monitor to !-- reference the user-defined flow !-- record ! flow monitor FLOW-MONITOR-ipv6 record FLOW-RECORD-ipv6 ! !-- Apply the flow monitor to the interface !-- in the ingress direction ! interface GigabitEthernet0/0 ipv6 flow monitor FLOW-MONITOR-ipv6 input
The Cisco IOS Flexible NetFlow flow output is as follows:
router#show flow monitor FLOW-MONITOR-ipv6 cache format table Cache type: Normal Cache size: 4096 Current entries: 6 High Watermark: 2 Flows added: 539 Flows aged: 532 - Active timeout ( 1800 secs) 350 - Inactive timeout ( 15 secs) 182 - Event aged 0 - Watermark aged 0 - Emergency aged 0 IPV6 SRC ADDR ipv6 dst addr trns src port trns dst port intf input intf output pkts ip prot ================= ================= ============= ============= ========== =========== ==== ======= 2001:DB...06::201 2001:DB...28::20 123 123 Gi0/0 Gi0/0 17 17 2001:DB...06::201 2001:DB...28::20 1265 5060 Gi0/0 Gi0/0 1237 6 2001:DB...06::201 2001:DB...28::20 1441 5060 Gi0/0 Gi0/0 2346 6 2001:DB...06::201 2001:DB...28::20 1890 5061 Gi0/0 Gi0/0 5009 6 2001:DB...06::201 2001:DB...28::20 2856 5060 Gi0/0 Gi0/0 486 17 2001:DB...06::201 2001:DB...28::20 3012 53 Gi0/0 Gi0/0 1016 17 2001:DB...06::201 2001:DB...28::20 2477 53 Gi0/0 Gi0/0 1563 17To permit display of the full 128-bit IPv6 address, use the terminal width 132 exec mode command.
To view only the packets on TCP port 5060 and 5061, use the show flow monitor FLOW-MONITOR-ipv6 cache format table | include IPV6 DST ADDR|_(5060|5061)_.*_6_ command to display the related Cisco IOS Flexible NetFlow records.
Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls
Mitigation: Transit Access Control Lists
To protect the network from traffic that enters the network at ingress access points, which may include Internet connection points, partner and supplier connection points, or VPN connection points, administrators are advised to deploy tACLs to perform policy enforcement. Administrators can construct a tACL by explicitly permitting only authorized traffic to enter the network at ingress access points or permitting authorized traffic to transit the network in accordance with existing security policies and configurations. A tACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The tACL policy denies unauthorized IPv4 and IPv6 packets on TCP port 5060 and TCP port 5061 that are sent to affected devices. In the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP address space that is used by the affected devices, and the hosts at 192.168.100.1 and 2001:DB8::100:1 are considered trusted sources that require access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.
Additional information about tACLs is in Transit Access Control Lists: Filtering at Your Edge.
! !-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable TCP ports protocol ! access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5060 access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5061 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 5060 access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 5061 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Explicit deny for all other IP traffic ! access-list tACL-Policy extended deny ip any any ! !-- Create the corresponding IPv6 tACL ! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable TCP ports protocol ! ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:db8:1:60::/64 eq 5060 ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:db8:1:60::/64 eq 5061 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:db8:1:60::/64 eq 5060 ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:db8:1:60::/64 eq 5061 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Explicit deny for all other IP traffic ! ipv6 access-list IPv6-tACL-Policy deny ip any any ! !-- Apply tACLs to interfaces in the ingress direction ! access-group tACL-Policy in interface outside access-group IPv6-tACL-Policy in interface outside
Identification: Transit Access Control Lists
After the tACL has been applied to an interface, administrators can use the show access-list command to identify the number of IPv4 and IPv6 packets on tcp port 5060 and 5061 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit this vulnerability. Example output for show access-list tACL-Policy and show access-list IPv6-tACL-Policy follows:
firewall#show access-list tACL-Policy access-list tACL-Policy; 5 elements; name hash: 0x3452703d access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq sip (hitcnt=31) access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=61) access-list tACL-Policy line 3 extended deny tcp any 192.168.60.0 255.255.255.0 eq sip (hitcnt=8) access-list tACL-Policy line 4 extended deny tcp any 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=14) access-list tACL-Policy line 5 extended deny ip any any (hitcnt=8)In the preceding example, access list tACL-Policy has dropped the following packets received from an untrusted host or network:
- 8 packets on tcp port 5060 for ACE line 3
- 14 packets on tcp port 5061 for ACE line 4
firewall#show access-list IPv6-tACL-Policy ipv6 access-list IPv6-tACL-Policy; 5 elements; name hash: 0x566a4229 ipv6 access-list IPv6-tACL-Policy line 1 permit tcp host 2001:db8:1:100::1 2001:db8:1:60::/64 eq sip (hitcnt=59) ipv6 access-list IPv6-tACL-Policy line 2 permit tcp host 2001:db8:1:100::1 2001:db8:1:60::/64 eq 5061 (hitcnt=28) ipv6 access-list IPv6-tACL-Policy line 3 deny tcp any 2001:db8:1:60::/64 eq sip (hitcnt=47) ipv6 access-list IPv6-tACL-Policy line 4 deny tcp any 2001:db8:1:60::/64 eq 5061 (hitcnt=33) ipv6 access-list IPv6-tACL-Policy line 5 deny ip any any (hitcnt=27)In the preceding example, access list IPv6-tACL-Policy has dropped the following packets received from an untrusted host or network:
- 47 packets on TCP port 5060 for ACE line 3
- 33 packets on TCP port 5061 for ACE line 4
In addition, syslog message 106023 can provide valuable information, which includes the source and destination IP address, the source and destination port numbers, and the IP protocol for the denied packet.
Identification: Firewall Access List Syslog Messages
Firewall syslog message 106023 will be generated for packets denied by an access control entry (ACE) that does not have the log keyword present. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 106023.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog on the Cisco Catalyst 6500 Series ASA Services Module is in Configuring Logging. Information about configuring syslog on the FWSM for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers is in Monitoring the Firewall Services Module.
In the following example, the show logging | grep regex command extracts syslog messages from the logging buffer on the firewall. These messages provide additional information about denied packets that could indicate potential attempts to exploit the vulnerabilities that are described in this document. It is possible to use different regular expressions with the grep keyword to search for specific data in the logged messages.
Additional information about regular expression syntax is in Creating a Regular Expression.
firewall#show logging | grep 106023 Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/2944 dst inside:192.168.60.191/5060 by access-group "tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2945 dst inside:192.168.60.33/5060 by access-group "tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.99/2946 dst inside:192.168.60.240/5060 by access-group "tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.100/2947 dst inside:192.168.60.115/5060 by access-group "tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.88/2949 dst inside:192.168.60.38/5060 by access-group "tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.175/2950 dst inside:192.168.60.250/5060 by access-group "tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:2001:db8:2::2:172/2951 dst inside:2001:db8:1:60::23/5060 by access-group "IPv6-tACL-Policy" Aug 21 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:2001:db8:d::a85e:172/2952 dst inside:2001:db8:1:60::134/5060 by access-group "IPv6-tACL-Policy" firewall#In the preceding example, the messages logged for the tACL tACL-Policy and IPv6-tACL-Policy show potentially spoofed packets for TCP port 5060 sent to the address block assigned to the affected devices.
Additional information about syslog messages for Cisco ASA Series Adaptive Security Appliances is in Cisco ASA 5500 Series System Log Messages, 8.2. Additional information about syslog messages for Cisco Catalyst 6500 Series ASA Services Module is in the Analyzing Syslog Messages section of the Cisco ASASM CLI Configuration Guide. Additional information about syslog messages for the Cisco FWSM is in Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Logging System Log Messages.
For additional information about investigating incidents using syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Cisco Security Intelligence Operations white paper.
Mitigation: Connection Limits
Limiting the number of embryonic connections helps protect networks from a DoS attack. The ASA uses the per-client limits and the embryonic connection limit to trigger TCP Intercept, which protects inside systems from a DoS attack perpetrated by flooding an interface with TCP SYN packets. An embryonic connection is a connection request that has not finished the necessary handshake between source and destination. TCP Intercept uses the SYN cookies algorithm to prevent TCP SYN-flooding attacks. A SYN-flooding attack consists of a series of SYN packets usually originating from spoofed IP addresses. The constant flood of SYN packets keeps the server SYN queue full, which prevents it from servicing connection requests. When the embryonic connection threshold of a connection is crossed, the ASA acts as a proxy for the server and generates a SYN-ACK response to the client SYN request. When the ASA receives an ACK back from the client, it can then authenticate the client and allow the connection to the server.
Administrators may construct an inspection policy for applications that require special handling through the configuration of inspection class maps and inspection policy maps, which are applied via a global or interface service policy.
Additional information about Connection Limits is in the Configuring Connection Limits and Timeouts section of the Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2 .
Caution: Administrators are advised to test performance impact of Connection Limits in a lab environment before this feature is deployed in production environments.
! !-- Configure the class-map, policy-map and service-policy !-- limit embryonic connections ! firewall(config)# class-map embryonic
firewall(config-cmap)# match any
firewall(config-cmap)# policy-map embryonic
firewall(config-pmap)# class embryonic
firewall(config-pmap-c)# set connection conn-max 1000 embryonic-conn-max 3000
firewall(config-pmap-c)# set connection timeout tcp 2:0:0 embryonic 0:40:0
half-closed 0:20:0 dcd
firewall(config-pmap-c)# service-policy embryonic interface outside
! !Identification: Connection Limits
With connection limits properly configured, administrators can use show commands to display statistical connection limit information on the Cisco ASA and Cisco ASASM. The following example shows the drops recorded by connection limit.
firewall# sh service-policy set connection detail | include conn
Set connection policy: conn-max 1000 embryonic-conn-max 3000
current embryonic conns 994, current conns 994, drop 8844541 firewall# sh threat-detection rate conn-limit-drop Average(eps) Current(eps) Trigger Total events
10-min Conn limt: 14712 0 25 8827467
1-hour Conn limt: 2456 0 5 8844390In the preceding example, the output from the command show service-policy set connection detail | include conn displays 8,884,541 dropped connections to the affected devices. the output from the command show threat-detection rate conn-limit-drop will display counters for connection limit dropped packets over time.
Identification: Threat Detection
Cisco Adaptive Security Appliance supports the threat detection feature in software releases 8.0 and later. Using basic threat detection, the security appliance monitors the rate of dropped packets and security events with the following reasons:
- Denial by access lists
- Bad packet format (such as invalid-ip-header or invalid-tcp-hdr-length)
- Connection limits exceeded (both system-wide resource limits and limits set in the configuration)
- DoS attack detected (such as an invalid stateful packet inspection (SPI), Stateful Firewall check failure)
- Basic firewall checks failed (This option is a combined rate that includes all firewall-related packet drops in this bulleted list. It does not include non-firewall-related drops such as interface overload, packets failed at application inspection, and scanning attack detected.)
- Suspicious ICMP packets detected
- Packets failed application inspection
- Interface overload
- Scanning attack detected (This option monitors scanning attacks; for example, the first TCP packet is not a SYN packet, or the TCP connection failed the three-way handshake. Full scanning threat detection [refer to Configuring Scanning Threat Detection for more information] takes this scanning attack rate information and acts on it by classifying hosts as attackers and automatically shunning them, for example.)
- Incomplete session detection such as TCP SYN attack detected or no data UDP session attack detected.
Caution: Configuring advanced threat detection statistics can have a significant impact on the device''s CPU.
More information about configuring threat detection for the Cisco ASA 5500 Series Adaptive Security Appliance is in Configuring Threat Detection. Information about configuring threat detection for the Cisco Catalyst 6500 Series ASA Services Module is in Configuring Threat Detection.
To enable Threat Detection, enter the threat-detection basic-threat command.With basic threat detection properly configured, administrators can use the sh threat-detection rate conn-limit-drop command to show the threat events the Cisco ASA or Cisco ASASM has detected. The following example shows 20 SYN attack-related events per second and 223 SYN Trigger events occurring within the burst interval, and 30 Scanning attack-related events and 451 Scanning Trigger events occurring within the burst interval, and 28471 Connection Limit events in the burst interval, which could be an indication of an ongoing SYN flood.
firewall# show threat-detection rate Average(eps) Current(eps) Trigger Total events 10-min ACL drop: 1 10 0 983 1-hour ACL drop: 0 0 0 983 10-min SYN attck: 2 20 223 1982 1-hour SYN attck: 0 0 87 1982 10-min Scanning: 3 30 451 2269 1-hour Scanning: 0 0 154 2269
10-min Conn limt: 37923 28471 141 22754052
1-hour Conn limt: 12132 31485 58 43677273
10-min Bad pkts: 0 0 0 4 1-hour Bad pkts: 0 0 0 4 10-min Firewall: 1 10 0 987 1-hour Firewall: 0 0 0 987 10-min Interface: 1 0 0 851 1-hour Interface: 0 0 0 851 firewall#Mitigation: Spoofing Protection Using Unicast Reverse Path Forwarding
The vulnerabilities that are described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure uRPF as a protection mechanism against spoofing.
uRPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on uRPF to provide complete spoofing protection because spoofed packets may enter the network through a uRPF-enabled interface if an appropriate return route to the source IP address exists. In an enterprise environment, uRPF may be enabled at the Internet edge and at the internal access layer on the user-supporting Layer 3 interfaces.
For additional information about the configuration and use of uRPF, reference the Cisco Security Appliance Command Reference for ip verify reverse-path and the Understanding Unicast Reverse Path Forwarding Cisco Security white paper.
Identification: Spoofing Protection Using Unicast Reverse Path Forwarding
Firewall syslog message 106021 will be generated for packets denied by uRPF. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 106021.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog for the Cisco Catalyst 6500 Series ASA Services Module is in Configuring Logging. Information about configuring syslog on the FWSM for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers is in Monitoring the Firewall Services Module.
In the following example, the show logging | grep regex command extracts syslog messages from the logging buffer on the firewall. These messages provide additional information about denied packets that could indicate potential attempts to exploit the vulnerabilities that are described in this document. It is possible to use different regular expressions with the grep keyword to search for specific data in the logged messages.
Additional information about regular expression syntax is in Creating a Regular Expression.
firewall#show logging | grep 106021 Aug 21 2013 00:15:13: %ASA-1-106021: Deny TCP reverse path check from 192.168.60.1 to 192.168.60.100 on interface outside Aug 21 2013 00:15:13: %ASA-1-106021: Deny TCP reverse path check from 192.168.60.1 to 192.168.60.100 on interface outside Aug 21 2013 00:15:13: %ASA-1-106021: Deny TCP reverse path check from 192.168.60.1 to 192.168.60.100 on interface outsideThe show asp drop command can also identify the number of packets that the uRPF feature has dropped, as shown in the following example:
firewall#show asp drop frame rpf-violated Reverse-path verify failed 11 firewall#
In the preceding example, uRPF has dropped 11 IP packets received on interfaces with uRPF configured. Absence of output indicates that the uRPF feature on the firewall has not dropped packets.
For additional information about debugging accelerated security path dropped packets or connections, reference the Cisco Security Appliance Command Reference for show asp drop.
Cisco Security Manager
Identification: Cisco Security Manager
Cisco Security Manager, Event Viewer
Beginning in software version 4.0, Cisco Security Manager can collect syslogs from Cisco firewalls and Cisco IPS devices and provides the Event Viewer, which can query for events that are related to the vulnerabilities that are described in this document.
Using the following filters in the Firewall Denied Events predefined view in the Event Viewer provides all captured Cisco firewall access list deny syslog messages that could indicate potential attempts to exploit the vulnerabilities that are described in this document.
- Use the Destination event filter to filter network objects that contain the IP address space that is used by the affected devices (for example, IPv4 address range 192.168.60.0/24 and IPv6 address range 2001:DB8:1:60::/64)
- Use the Destination Service event filter to filter objects that contain TCP port 5060 or 5061
An Event Type ID filter can be used with the Firewall Denied Events predefined view in the Event Viewer to filter the syslog IDs shown in the following list to provide all captured Cisco firewall deny syslog messages that could indicate potential attempts to exploit the vulnerabilities that are described in this document:
- ASA-4-106021 (uRPF spoofing)
- ASA-4-106023 (ACL deny)
- ASA-4-733100 (Object drop rate exceeded)
For more information about Cisco Security Manager Events, refer to the Filtering and Querying Events section of the Cisco Security Manager User Guide.
Identification: Event Management System Partner Events
Cisco works with industry-leading Security Information and Event Management (SIEM) companies through the Cisco Developer Network. This partnership helps Cisco deliver validated and tested SIEM systems that address business concerns such as long-term log archiving and forensics, heterogeneous event correlation, and advanced compliance reporting. Security Information and Event Management partner products can be leveraged to collect events from Cisco devices and then query the collected events for the incidents created by a Cisco IPS signature or deny syslog messages from firewalls that could indicate potential attempts to exploit the vulnerabilities that are described in this document. The queries can be made by Sig ID and Syslog ID as shown in the following list:
- ASA-4-106021 (uRPF spoofing)
- ASA-4-106023 (ACL deny)
- ASA-4-733100 (Object drop rate exceeded)
For more information about SIEM partners, refer to the Security Management System website.
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THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
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Show LessVersion Description Section Date 1 Initial Release
2013-August-21 16:02 GMT
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Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.
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The security vulnerability applies to the following combinations of products.
Primary Products Cisco Cisco Unified Communications Manager IM and Presence Service 9.0 ((1)) | 9.1 ((1))
Associated Products
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THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy and may lack important information or contain factual errors. The information in this document is intended for end users of Cisco products