Cisco Security Advisory
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AV:N/AC:L/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
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The Cisco Content Switching Module (CSM) and Cisco Content Switching Module with SSL (CSM-S) contain a memory leak vulnerability that can result in a denial of service condition. The vulnerability exists when the CSM or CSM-S is configured for layer 7 load balancing. An attacker can trigger this vulnerability when the CSM or CSM-S processes TCP segments with a specific combination of TCP flags while servers behind the CSM/CSM-S are overloaded and/or fail to accept a TCP connection.
Cisco has released software updates that address this vulnerability.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080514-csm.
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Vulnerable Products
The Cisco CSM and Cisco CSM-S are affected by the vulnerability described in this document if they are running an affected software version and are configured for layer 7 load balancing.
The following versions of the Cisco CSM software are affected by this vulnerability: 4.2(3), 4.2(3a), 4.2(4), 4.2(5), 4.2(6), 4.2(7), and 4.2(8).
The following versions of the Cisco CSM-S software are also affected by this vulnerability: 2.1(2), 2.1(3), 2.1(4), 2.1(5), 2.1(6), and 2.1(7).
To determine the software version in use by the CSM or CSM-S, log into the supervisor of the chassis that hosts the CSM or CSM-S modules and issue the command show module version (Cisco IOS) or show version (Cisco CatOS). CSM modules will display as model "WS-X6066-SLB-APC", CSM-S modules will display as model "WS-X6066-SLB-S-K9", and the software version will be indicated next to the "Sw:" label.
Note that the output from show module version (for Cisco IOS) is slightly different from the output from show version (for Cisco CatOS). However, in both cases the model names will read as previously described, and the software version will be easily identified by looking for the "Sw:" label.
The following example shows a CSM in slot number 4 running software version 4.2(3):
switch>show module version Mod Port Model Serial # Versions ---- ---- ------------------ ----------- ------------------------------------- 1 3 WS-SVC-AGM-1-K9 SAD092601W5 Hw : 1.0 Fw : 7.2(1) Sw : 5.0(3) 2 6 WS-SVC-FWM-1 SAD093200X8 Hw : 3.0 Fw : 7.2(1) Sw : 3.2(3)1 3 8 WS-SVC-IDSM-2 SAD0932089Z Hw : 5.0 Fw : 7.2(1) Sw : 5.1(6)E1 4 4 WS-X6066-SLB-APC SAD093004BD Hw : 1.7 Fw : Sw : 4.2(3) 5 2 WS-SUP720-3B SAL0934888E Hw : 4.4 Fw : 8.1(3) Sw : 12.2(18)SXF11 Sw1: 8.6(0.306)R3V15 WS-SUP720 SAL09348488 Hw : 2.3 Fw : 12.2(17r)S2 Sw : 12.2(18)SXF11 WS-F6K-PFC3B SAL0934882R Hw : 2.1A Cisco CSM or CSM-S is configured for layer 7 load balancing if one or more layer 7 Server Load Balancing (SLB) policies are referenced in the configuration of a virtual server. There are six possible types of SLB policies: "client-group", "cookie-map", "header-map", "reverse-sticky", "sticky-group", and "url-map". Of these, the "client-group" policy type is always a layer 4 policy. The remaining policy types are layer 7 policies and, if used, would render a device affected by the vulnerability described in this document. The following example shows a CSM module that is configured for layer 7 load balancing. Note the SLB policy "TEST-SPORTS-50", which uses "url-map" and "header-map" layer 7 policies, and that is applied to the virtual server named "WEB":
module ContentSwitchingModule 5 [...] ! policy TEST-SPORTS-50 url-map SPORTS header-map TEST client-group 50 serverfarm WEBFARM2 ! vserver WEB virtual 10.20.221.100 tcp www serverfarm WEBFARM persistent rebalance slb-policy TEST-SPORTS-50 inservice
Products Confirmed Not Vulnerable
Only Cisco CSM modules running indicated 4.2 versions are affected by this vulnerability. CSM software versions 4.1, 3.2 and 3.1 are not affected by this vulnerability.
Cisco CSM-S modules running indicated 2.1 versions are the only vulnerable versions of software for that product.
Cisco CSM and CSM-S modules that are not configured for layer 7 load balancing are not affected by this vulnerability.
The Cisco IOS SLB feature is not affected by this vulnerability.
No other Cisco products are currently known to be affected by this vulnerability. The Cisco Secure Content Accelerator is not affected by this vulnerability.
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The Cisco CSM is an integrated SLB line card for the Catalyst 6500 and 7600 Series that is designed to enhance the response time for client traffic to end points including servers, caches, firewalls, Secure Sockets Layer (SSL) devices, and VPN termination devices.
The Cisco CSM-S combines high-performance SLB with SSL offload. The CSM-S is similar to the CSM; however, unlike the CSM, the CSM-S can terminate and initiate SSL-encrypted traffic. This ability allows the CSM-S to perform intelligent load balancing while ensuring secure end-to-end encryption.
A memory leak vulnerability exists in some versions of the software for the Cisco CSM and Cisco CSM-S when the CSM or CSM-S is configured for layer 7 load balancing (see the "Vulnerable Products" section for configuration details). The memory leak is triggered when the CSM or CSM-S processes TCP segments with a specific combination of TCP flags and fails to make a load balancing decision because servers behind the CSM/CSM-S are overloaded and/or fail to accept a TCP connection.
The memory leak can be detected by issuing the command show module ContentSwitchingModule <slot #> tech-support all | include Outstanding on the supervisor and checking the command output for a high number of outstanding buffers as seen in the following example:
switch#show module ContentSwitchingModule 10 tech-support all | include Outstanding Outstanding slowpath(low pri) buffers 0 0 Outstanding slowpath(high pri) buffers 0 0 Outstanding blocks 0 0 Outstanding small buffers 0 0 Outstanding medium buffers 823 0 Outstanding large buffers 0 0 Outstanding sessions 0 0 Outstanding Closes 0 0 Close Relinquish Outstanding 0
Because small, medium, and large buffers can be affected by the memory leak, administrators are advised to check the number of these buffers in the output from the preceding command to accurately detect a memory leak condition.
This vulnerability is documented in Cisco Bug ID CSCsl40722 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-1749.
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There are no workarounds for this vulnerability. When the Cisco CSM or Cisco CSM-S has run out of memory it will simply stop passing traffic and it will have to be reloaded. The CSM and CSM-S can be reloaded via the command hw-module module <CSM or CSM-S slot number> reset (Cisco IOS) or via the command reset <CSM or CSM-S slot number> (Cisco CatOS) from the privileged EXEC prompt of the supervisor. There is no need to reload the supervisor.
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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.
This vulnerability is fixed in version 4.2.9 of the Cisco CSM software, and in version 2.1.8 of the Cisco CSM-S software.
CSM software can be downloaded from http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-csm?psrtdcat20e2 ( registered customers only) .
Information on how to upgrade the CSM software is available at http://www.cisco.com/en/US/products/hw/modules/ps2706/products_tech_note09186a0080094526.shtml.
CSM-S software can be downloaded from http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-csms?psrtdcat20e2 ( registered customers only) .
Information on how to upgrade the CSM-S software is available at http://www.cisco.com/en/US/docs/interfaces_modules/services_modules/csms/2.1.1/configuration/guide/getstart.html#wp1041858.
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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 discovered during the investigation of customer support cases.
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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 1.0
2008-May-14
Initial public release
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