Cisco Applied Mitigation Bulletin-
A vulnerability in the Nano-10 programmable logic controller (PLC) could cause a denial of service (DoS) condition on a targeted device.
The vulnerability exists because the affected software does not perform sufficient boundary checks on user-supplied input when processing TCP packets. An unauthenticated, remote attacker could exploit the vulnerability by submitting malicious TCP packets to a targeted device. A successful exploit could allow the attacker to cause the targeted application to become inaccessible from the network, resulting in a DoS condition.
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Vulnerability Characteristics
Details of this vulnerability are described in Alert 29981.
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Vulnerability Overview
ICS-CERT has re-released a security advisory at the following link: http://ics-cert.us-cert.gov/advisories/ICSA-13-189-02.
Information on field replaceable units is available from the Triangle Research Technical Inquiries page at http://www.triplc.com/techinq.htm.
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Cisco IOS Software can provide effective means of exploit prevention using transit access control lists (tACLs).
This protection mechanism filters and drops packets that are attempting to exploit this vulnerability.
Effective 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 tACLs.
This protection mechanism filters and drops packets that are attempting to exploit the vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.
Cisco IOS Software, Cisco ASA, Cisco ASASM, and Cisco FWSM firewalls can provide visibility through syslog messages and counter values displayed in the output from show commands.
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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
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 MODBUS IPv4 packets on TCP port 502 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 available in Transit Access Control Lists: Filtering at Your Edge.
!-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable port ! access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 502 ! !-- The following vulnerability-specific access control entry !-- (ACEs) can aid in identification of attacks ! access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 502 ! !-- 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 ! !-- Apply tACL to interface in the ingress direction ! interface GigabitEthernet0/0 ip access-group 150 in
Note 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 command no ip unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration command ip icmp rate-limit unreachable interval-in-ms .
Identification: Transit Access Control Lists
After the administrator applies the tACL to an interface, show ip access-lists command will identify the number of MODBUS IPv4 packets on TCP port 502 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 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 502 20 deny tcp any 192.168.60.0 0.0.0.255 eq 502 (40 matches) 30 deny ip any any router#In the preceding example, access list 150 has dropped 40 MODBUS packets on TCP port 502 for access control list entry (ACE) line 20.
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 Intelligence Operations white paper.
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 the vulnerability described in this document. Administrators are advised to investigate flows to determine whether they are attempts to exploit the 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 5004 01F6 40 Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 06 5005 01F6 23 Gi0/1 192.168.150.60 Gi0/0 10.89.16.226 06 0016 0050 1 Gi0/0 192.168.13.97 Gi0/1 192.168.60.28 06 5006 01F6 15 Gi0/0 192.168.10.17 Gi0/1 192.168.60.97 06 5007 01F6 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 00A2 1 Gi0/0 10.89.16.226 Gi0/1 192.168.150.60 06 12CA 0016 1In the preceding example, there are multiple flows for MODBUS on TCP port 502 (hex value 01F6).
As shown in the following example, to view only the traffic flows for MODBUS packets on TCP port 502 (hex value 01F6), use the show ip cache flow | include SrcIf|_06_.*01F6 command to display the related Cisco NetFlow records:
TCP Flowsrouter#show ip cache flow | include SrcIf|_06_.*01F6 SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.12.110 Gi0/1 192.168.60.163 06 5380 01F6 17 Gi0/0 192.168.11.230 Gi0/1 192.168.60.20 06 5381 01F6 91 Gi0/0 192.168.11.131 Gi0/1 192.168.60.245 06 5382 01F6 108 Gi0/0 192.168.13.7 Gi0/1 192.168.60.162 06 5383 01F6 31 Gi0/0 192.168.41.86 Gi0/1 192.168.60.27 06 5384 01F6 9
Identification: IPv4 Traffic Flow Identification Using Cisco IOS 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 5540 502 Gi0/0 Gi0/1 937 6 192.168.11.54 192.168.60.158 123 123 Gi0/0 Gi0/1 2212 17 192.168.150.60 10.89.16.226 2567 443 Gi0/0 Gi0/1 13 6 192.168.13.97 192.168.60.28 5541 502 Gi0/0 Gi0/1 88 6 192.168.10.17 192.168.60.97 5542 502 Gi0/0 Gi0/1 9 6 10.88.226.1 192.168.202.22 2678 53 Gi0/0 Gi0/1 8567 17 10.89.16.226 192.168.150.60 3562 80 Gi0/0 Gi0/1 4012 6To view only the MODBUS on TCP port 502, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_502.*_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 15.1M&T and Cisco IOS Flexible NetFlow Configuration Guide, Release 12.4T.
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 MODBUS IPv4 packets on TCP port 502 that are sent to affected devices. In the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 is 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 protocols and ports ! access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 502 ! !-- The following vulnerability-specific ACEs !-- can aid in identification of attacks ! access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 502 ! !-- 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 ! !-- Apply tACLs to interfaces in the ingress direction ! access-group 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 MODBUS IPv4 packets on TCP port 502 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 follows:
firewall#show access-list tACL-Policy access-list tACL-Policy; 3 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 502 (hitcnt=18) access-list tACL-Policy line 2 extended deny tcp any 192.168.60.0 255.255.255.0 eq 502 (hitcnt=34) access-list tACL-Policy line 3 extended deny ip any any (hitcnt=3)In the preceding example, access list tACL-Policy has dropped 34 MODBUS packets on TCP port 502 received from an untrusted host or network. 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.
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 vulnerability that is 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 Jul 12 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/5534 dst inside:192.168.60.191/502 by access-group "tACL-Policy" Jul 12 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/5535 dst inside:192.168.60.33/502 by access-group "tACL-Policy" Jul 12 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.99/5536 dst inside:192.168.60.240/502 by access-group "tACL-Policy" Jul 12 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.100/5537 dst inside:192.168.60.115/502 by access-group "tACL-Policy" firewall#In the preceding example, the messages logged for the tACL tACL-Policy show MODBUS packets for TCP port 502 sent to the address block assigned to 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.
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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-July-12 21:38 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 IntelliShield Security Activity Bulletin Original Release (Base)
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