AV:N/AC:L/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
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The Cisco IOS Intrusion Prevention System (IPS) feature contains a vulnerability in the processing of certain IPS signatures that use the SERVICE.DNS engine. This vulnerability may cause a router to crash or hang, resulting in a denial of service condition.
Cisco has released software updates that address this vulnerability. There is a workaround for this vulnerability.
Note: This vulnerability is not related in any way to CVE-2008-1447 - Cache poisoning attacks. Cisco Systems has published a Cisco Security Advisory for that vulnerability, which can be found at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080708-dns.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosips.
Note: The September 24, 2008 IOS Advisory bundled publication includes twelve Security Advisories. Eleven of the advisories address vulnerabilities in Cisco's IOS software, and one advisory addresses vulnerabilities in Cisco Unified Communications Manager. Each Advisory lists the releases that correct the vulnerability described in the Advisory.
Individual publication links are listed below:
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-sip
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-cucm
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-vpn
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-mfi
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ipc
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ubr
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-multicast
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-sccp
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosfw
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-l2tp
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https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl
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Vulnerable Products
Any Cisco IOS device configured with the Cisco IOS IPS feature is vulnerable, regardless if it is configured to use the built-in signatures or an external signature file. Devices using either version 4 or version 5 signatures are affected by this vulnerability.
The Cisco IOS IPS feature is not enabled by default. The command show ip ips interfaces can be used to determine if the Cisco IOS IPS feature has been configured and applied to any interface on the device, as in the following example:
Router#show ip ips interfaces Interface Configuration Interface FastEthernet0/0 Inbound IPS rule is ios-ips-incoming Outgoing IPS rule is not set Interface FastEthernet0/1 Inbound IPS rule is not set Outgoing IPS rule is ios-ips-outgoing Router#
The output of the show ip ips interfaces command when the Cisco IOS IPS feature has not been configured is dependent on which Cisco IOS release is installed and running on the device. It may be similar to the following example:
Router#show ip ips interfaces Router#
or it may be similar to the following:
Router#show ip ips interfaces Interface Configuration IPS is not configured on any interface Router#
Any version of Cisco IOS prior to the versions which are listed in the Software Versions and Fixes section below is vulnerable.
To determine the version of the Cisco IOS software running on a Cisco product, log in to the device and issue the show version command to display the system banner. Cisco IOS software will identify itself as "Internetwork Operating System Software" or simply "IOS". On the next line of output, the image name will be displayed between parentheses, followed by "Version" and the IOS release name. Other Cisco devices will not have the show version command or will give different output.
The following example identifies a Cisco product running Cisco IOS Software release 12.3(26) with an installed image name of C2500-IS-L:
Router#show version Cisco Internetwork Operating System Software IOS (tm) 2500 Software (C2500-IS-L), Version 12.3(26), RELEASE SOFTWARE (fc2) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2008 by cisco Systems, Inc. Compiled Mon 17-Mar-08 14:39 by dchih <output truncated> Router#
The next example shows a product running Cisco IOS Software release 12.4(20)T with an image name of C1841-ADVENTERPRISEK9-M:
Router#show version Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 12.4(20)T, RELEASE SOFTWARE (fc3) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2008 by Cisco Systems, Inc. Compiled Thu 10-Jul-08 20:25 by prod_rel_team <output truncated> Router#
Additional information on the Cisco IOS release naming conventions can be found on the document entitled "White Paper: Cisco IOS Reference Guide", which is available at http://www.cisco.com/warp/public/620/1.html.
Products Confirmed Not Vulnerable
The following Cisco products are confirmed not vulnerable:
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Cisco IOS devices running the Intrusion Detection System
feature
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Cisco ASA Security Appliances running the Intrusion Detection System
feature
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Cisco PIX 500 Series Security Appliances running the Intrusion
Detection System feature
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Cisco IPS 4200 Sensors
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Cisco AIP-SSM for ASA 5500 Series Adaptive Security Appliances
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Cisco Catalyst 6500 Series Intrusion detection System (IDSM-2)
Services Module
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Cisco IPS Advanced Integration Module for Integrated Services
Routers
No other Cisco products are currently known to be affected by this vulnerability.
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Cisco IOS devices running the Intrusion Detection System
feature
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Cisco IOS Intrusion Prevention System (IPS) is an inline, deep-packet inspection feature that effectively mitigates a wide range of network attacks. A component of the Cisco IOS Integrated Threat Control framework and complemented by Cisco IOS Flexible Packet Matching feature, Cisco IOS IPS provides your network with the intelligence to accurately identify, classify, and stop or block malicious traffic in real time. Additional information on the Cisco IOS IPS feature can be found at http://www.cisco.com/en/US/docs/ios/12_3t/12_3t8/feature/guide/gt_fwids.html.
Previous to the introduction of the Cisco IOS IPS feature, Cisco IOS provided a similar feature, the Cisco IOS Intrusion Detection System (IDS). The Cisco IOS IDS feature is not affected by this vulnerability. Additional information on the Cisco IOS IDS feature can be found at http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/ios_ids.html.
Certain network traffic can trigger IPS signatures on the SERVICE.DNS signature engine which may cause the Cisco IOS device to crash or hang. This may cause a denial of service that results in disruption of network traffic. This vulnerability is documented in Cisco Bug ID CSCsq13348 ( registered customers only) .
This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-2739.
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The workaround consists of adding an Access Control List (ACL) to every Cisco IOS IPS policy configured on the device so that traffic destined to ports 53/udp or 53/tcp is not inspected by the Cisco IOS IPS feature. The following ACL would need to be added to the device configuration:
! deny inspection of traffic with a destination port of 53/udp access-list 177 deny udp any any eq 53 ! deny inspection of traffic with a destination port of 53/tcp access-list 177 deny tcp any any eq 53 ! allow all other traffic to be inspected access-list 177 permit ip any any
Every instance of a Cisco IOS IPS policy on the device would then need to be modified in order to reference the previous ACL. In order to determine which Cisco IOS IPS policies are configured on the device, execute the command show running-config | include ip ips name as in the following example:
Router#show running-config | include ip ips name ip ips name ios-ips-incoming ip ips name ios-ips-outgoing Router#
In the previous example, two Cisco IOS IPS policies are configured on the device. The following example shows the addition of an ACL to each one of the Cisco IOS IPS policies previously identified:
Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#ip ips name ios-ips-incoming list 177 Router(config)#ip ips name ios-ips-outgoing list 177 Router(config)#end Router#
As a verification step, the command show ip ips interfaces can be executed again to verify the ACL has been properly attached to each one of the Cisco IOS IPS policies:
Router#show ip ips interfaces Interface Configuration Interface FastEthernet0/0 Inbound IPS rule is ios-ips-incoming acl list 177 Outgoing IPS rule is not set Interface FastEthernet0/1 Inbound IPS rule is not set Outgoing IPS rule is ios-ips-outgoing acl list 177 Router#
Note: Disabling or deleting individual or all signatures using the SERVICE.DNS engine of the Cisco IOS IPS feature is not a recommended workaround. The previous workaround is the only Cisco-recommended workaround for this vulnerability.
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When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.
Each row of the Cisco IOS software table (below) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.
Major Release
Availability of Repaired Releases
Affected 12.0-Based Releases
First Fixed Release
Recommended Release
There are no affected 12.0 based releases
Affected 12.1-Based Releases
First Fixed Release
Recommended Release
There are no affected 12.1 based releases
Affected 12.2-Based Releases
First Fixed Release
Recommended Release
There are no affected 12.2 based releases
Affected 12.3-Based Releases
First Fixed Release
Recommended Release
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Not Vulnerable
Not Vulnerable
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Not Vulnerable
Not Vulnerable
Vulnerable; first fixed in 12.4
12.4(15)T7
12.4(18c)
Vulnerable; first fixed in 12.4T
12.4(15)T7
Not Vulnerable
Releases prior to 12.3(8)YG7 are vulnerable, release 12.3(8)YG7 and later are not vulnerable; first fixed in 12.4T
12.4(15)T7
Vulnerable; first fixed in 12.4T
12.4(15)T7
Vulnerable; first fixed in 12.4T
12.4(15)T7
Not Vulnerable
Vulnerable; first fixed in 12.4T
12.4(15)T7
12.3(14)YM13; Available on 30-SEP-08
12.3(14)YM13; Available on 30-SEP-08
Not Vulnerable
Vulnerable; first fixed in 12.4T
12.4(15)T7
Vulnerable; first fixed in 12.4T
12.4(15)T7
Not Vulnerable
Not Vulnerable
Vulnerable; contact TAC
Vulnerable; first fixed in 12.4T
12.4(15)T7
Affected 12.4-Based Releases
First Fixed Release
Recommended Release
12.4(18b)
12.4(19a)
12.4(21)
12.4(18c)
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
12.4(19)MR
12.4(19)MR
Not Vulnerable
12.4(15)T6
12.4(20)T
12.4(15)T7
Vulnerable; first fixed in 12.4T
12.4(15)T7
Not Vulnerable
Vulnerable; first fixed in 12.4T
12.4(15)T7
12.4(4)XD11; Available on 26-SEP-08
12.4(4)XD11; Available on 26-SEP-08
Vulnerable; first fixed in 12.4T
12.4(15)T7
Vulnerable; first fixed in 12.4T
12.4(15)T7
Not Vulnerable
Vulnerable; first fixed in 12.4T
12.4(15)T7
Vulnerable; first fixed in 12.4T
12.4(15)T7
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Not Vulnerable
Vulnerable; first fixed in 12.4T
12.4(15)T7
Vulnerable; contact TAC
12.4(11)XW9
12.4(11)XW9
12.4(15)XY4
12.4(15)XY4
12.4(15)XZ2
12.4(15)XZ2
12.4(20)YA1
12.4(20)YA1
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.
This vulnerability was reported to Cisco by a customer.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Revision 1.1
2009-April-16
Removed references to the combined software table, as it is now outdated
Revision 1.0
2008-September-24
Initial public release
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