This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Default Credentials for root Account on the Cisco Media Experience Engine 5600 and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
The Cisco Media Experience Engine (MXE) 5600 contains a root administrator account that is enabled by default with a default password. This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may allow arbitrary code execution or allow information disclosure, which enables an attacker to learn information about the affected device. The attack vector for exploitation is through SSH packets using TCP port 22 and Telnet packets using TCP port 23. Note: Telnet is disabled by default on the Cisco MXE 5600 but can be used as a vector of exploitation if it is manually enabled on affected devices.
This vulnerability has been assigned CVE identifier CVE-2011-1623.
Information about vulnerable, unaffected, and fixed software is available in the PSIRT Security Advisory, which is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110601-mxe.
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 infrastructure access control lists (iACLs). 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 and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers using transit access control lists (tACLs).
This protection mechanism filters and drops packets that are attempting to exploit this vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.
Cisco IOS Software and Cisco ASA and FWSM firewalls can provide visibility through syslog messages and counter values displayed in the output from show commands.
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.
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:
To protect infrastructure devices and minimize the risk, impact, and effectiveness of direct infrastructure attacks, administrators are advised to deploy infrastructure access control lists (iACLs) to perform policy enforcement of traffic sent to infrastructure equipment. Administrators can construct an iACL by explicitly permitting only authorized traffic sent to infrastructure devices in accordance with existing security policies and configurations. For the maximum protection of infrastructure devices, deployed iACLs should be applied in the ingress direction on all interfaces to which an IP address has been configured. An iACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The iACL policy denies unauthorized SSH packets on TCP port 22 and Telnet packets on TCP port 23 that are sent to affected devices. In the following example, 192.168.60.0/24 is the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic. Whenever possible, infrastructure address space should be distinct from the address space used for user and services segments. Using this addressing methodology will assist with the construction and deployment of iACLs.
Additional information about iACLs is in Protecting Your Core: Infrastructure Protection Access Control Lists.
ip access-list extended Infrastructure-ACL-Policy ! !-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable ports ! permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 22 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 23 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! deny tcp any 192.168.60.0 0.0.0.255 eq 22 deny tcp any 192.168.60.0 0.0.0.255 eq 23 ! !-- Explicit deny ACE for traffic sent to addresses configured within !-- the infrastructure address space ! deny ip any 192.168.60.0 0.0.0.255 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Apply iACL to interfaces in the ingress direction ! interface GigabitEthernet0/0 ip access-group Infrastructure-ACL-Policy 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.
After the administrator applies the iACL to an interface, the show ip access-lists command will identify the number of SSH packets on TCP port 22 and Telnet packets on TCP port 23 that have been filtered on interfaces on which the iACL is applied. Administrators should investigate filtered packets to determine whether they are attempts to exploit this vulnerability. Example output for show ip access-lists follows:
router#show ip access-lists Infrastructure-ACL-Policy
Extended IP access list Infrastructure-ACL-Policy
10 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq ssh
20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq telnet
30 deny tcp any 192.168.60.0 0.0.0.255 eq ssh (23 matches)
40 deny tcp any 192.168.60.0 0.0.0.255 eq telnet (17 matches)
50 deny ip any 192.168.60.0 0.0.0.255
router#
In the preceding example, access list Infrastructure-ACL-Policy has dropped 23 SSH packets on TCP port 22 for access control list entry (ACE) line 30 and 17 Telnet packets on TCP port 23 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 Applied Intelligence white paper.
Administrators can use Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Applied Intelligence white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of traffic flows that may be attempts to exploit the vulnerability. 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 (2409 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.349 .650 .000 .000 .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, 278544 bytes
89 active, 4007 inactive, 318 added
4544 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 34056 bytes
0 active, 1024 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-WWW 38 0.0 9 40 0.0 0.0 15.2
TCP-other 108 0.0 6 40 0.0 0.0 15.5
UDP-TFTP 10 0.0 4 28 0.0 0.0 15.7
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
UDP-other 73 0.0 7 28 0.0 0.0 15.5
Total: 229 0.0 7 35 0.0 0.0 15.5
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Et0/0 192.168.74.110 Et0/1 192.168.13.20 06 C8A7 D4BE 5
Et0/0 192.168.23.20 Et0/1 192.168.226.172 11 2123 540A 1
Et0/0 192.168.53.205 Et0/1 192.168.60.88 11 DEB7 0045 5
Et0/0 192.168.0.115 Et0/1 192.168.60.214 06 F73A 0050 11
Et0/0 192.168.0.30 Et0/1 192.168.60.63 06 A64E 0016 3
Et0/0 192.168.211.52 Et0/1 192.168.113.252 11 17AA 8F11 17
Et0/0 192.168.34.222 Et0/1 192.168.58.190 11 9A8F 2AD3 5
Et0/0 192.168.198.3 Et0/1 192.168.60.104 11 4F4D 0045 1
Et0/0 192.168.240.90 Et0/1 192.168.88.197 06 3D88 0017 15
Et0/0 192.168.0.96 Et0/1 192.168.60.126 06 9621 0017 3
Et0/0 192.168.155.22 Et0/1 192.168.80.13 06 1298 EB6A 10
Et0/0 192.168.0.20 Et0/1 192.168.60.78 06 1541 0050 3
Et0/0 192.168.0.2 Et0/1 192.168.60.195 06 5419 01BB 5
Et0/0 192.168.223.127 Et0/1 192.168.121.153 06 0613 17E5 7
Et0/0 192.168.0.28 Et0/1 192.168.60.101 06 B5C6 0017 2
Et0/0 192.168.92.207 Et0/1 192.168.43.167 11 1FF5 2815 11
Et0/0 192.168.0.28 Et0/1 192.168.60.139 06 24E9 0050 6
Et0/0 192.168.122.182 Et0/1 192.168.68.21 11 71C2 80BB 11
Et0/0 192.168.18.228 Et0/1 192.168.203.86 11 0630 77B4 16
Et0/0 192.168.0.218 Et0/1 192.168.60.248 06 531B 01BB 15
Et0/0 192.168.26.81 Et0/1 192.168.213.193 06 76D9 11B0 3
Et0/0 192.168.225.144 Et0/1 192.168.28.79 11 FF8F 299D 32
Et0/0 192.168.166.100 Et0/1 192.168.60.217 11 0B47 0045 10
Et0/0 192.168.49.15 Et0/1 192.168.139.203 11 D880 6D41 4
Et0/0 192.168.0.120 Et0/1 192.168.60.41 06 D24F 0016 6
Et0/0 192.168.0.109 Et0/1 192.168.60.189 06 B0B0 0016 11
Et0/0 192.168.0.65 Et0/1 192.168.60.136 06 6110 01BB 2
Et0/0 192.168.0.51 Et0/1 192.168.60.43 06 4090 0050 17
Et0/0 192.168.160.238 Et0/1 192.168.38.104 06 F54E DEE1 14
router#
In the preceding example, there are multiple flows for SSH on TCP port 22 (hex value 0016) and Telnet on TCP port 23 (hex value 0017).
To view only the traffic flows for SSH packets on TCP port 22 (hex value 0016) and Telnet packets on TCP port 23 (hex value 0017), the command show ip cache flow | include SrcIf|_06_.*0016|0017 will display the related TCP NetFlow records as shown here:
TCP Flows
router#show ip cache flow | include SrcIf|_06_.*0016|0017 SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Et0/0 192.168.0.30 Et0/1 192.168.60.63 06 A64E 0016 3 Et0/0 192.168.0.120 Et0/1 192.168.60.41 06 D24F 0017 6 Et0/0 192.168.0.109 Et0/1 192.168.60.189 06 B0B0 0016 11 router#
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 SSH packets on TCP port 22 and Telnet packets on TCP port 23 that are sent to affected devices. In the following example, 192.168.60.0/24 is the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires 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 ports
!
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 22
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 23
!
!-- 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 22
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 23
!
!-- 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 tACL to interface(s) in the ingress direction
!
access-group tACL-Policy in interface outside
After the tACL has been applied to an interface, administrators can use the show access-list command to identify the number of SSH packets on TCP port 22 and Telnet packets on TCP port 23 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; 5 elements access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq ssh (hitcnt=485) access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq telnet (hitcnt=29) access-list tACL-Policy line 3 extended deny tcp any 192.168.60.0 255.255.255.0 eq ssh (hitcnt=58) access-list tACL-Policy line 4 extended deny tcp any 192.168.60.0 255.255.255.0 eq telnet (hitcnt=16) access-list tACL-Policy line 5 extended deny ip any any (hitcnt=8) firewall#
In the preceding example, access list tACL-Policy has dropped 58 SSH packets on TCP port 22 and 16 Telnet packets on TCP port 23 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.
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 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 Jun 1 2011 07:32:32: %ASA-4-106023: Deny tcp src outside:192.0.2.1/1025 dst inside:192.168.60.194/22 by access-group "tACL-Policy" Jun 1 2011 07:32:32: %ASA-4-106023: Deny tcp src outside:192.0.2.1/1025 dst inside:192.168.60.164/22 by access-group "tACL-Policy" Jun 1 2011 07:32:32: %ASA-4-106023: Deny tcp src outside:192.0.2.1/1025 dst inside:192.168.60.106/23 by access-group "tACL-Policy" Jun 1 2011 07:32:32: %ASA-4-106023: Deny tcp src outside:192.0.2.1/1025 dst inside:192.168.60.241/23 by access-group "tACL-Policy" Jun 1 2011 07:32:32: %ASA-4-106023: Deny tcp src outside:192.0.2.169/1025 dst inside:192.168.60.56/22 by access-group "tACL-Policy" Jun 1 2011 07:32:32: %ASA-4-106023: Deny tcp src outside:192.0.2.36/1025 dst inside:192.168.60.202/22 by access-group "tACL-Policy" firewall#
In the preceding example, the messages logged for the tACL tACL-Policy show SSH packets for TCP port 22 and Telnet packets for TCP port 23 sent to the address block assigned to the infrastructure devices.
Additional information about syslog messages for ASA security appliances is in Cisco ASA 5500 Series System Log Messages, 8.2. Additional information about syslog messages for the 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 Applied Intelligence white paper.
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|
Revision 1.0 |
2011-June-01 |
Initial public release |
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