Summary

• The Cisco Internetwork Operating System (IOS) may permit arbitrary code execution after exploitation of a heap-based buffer overflow vulnerability. Cisco has included additional integrity checks in its software, as further described below, that are intended to reduce the likelihood of arbitrary code execution.

  Cisco has made free software available that includes the additional integrity checks for affected customers.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20051102-timers.

  Cisco is not aware of any active exploitation of this vulnerability. This advisory documents changes to Cisco IOS® as a result of continued research related to the demonstration of the exploit for another vulnerability which occurred in July 2005 at the Black Hat USA Conference. Cisco addressed the IPv6 attack vector used in that demonstration in a separate advisory published on July 29, 2005.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  This security advisory applies to all Cisco products that run Cisco IOS Software. Any version of Cisco IOS prior to the versions listed in the Fixed Software table below may be susceptible to heap overflow exploitation.

  To determine the 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 IOS release 12.3(6) with an installed image name of C3640-I-M:

  Cisco Internetwork Operating System Software
  IOS (tm) 3600 Software (C3640-I-M), Version 12.3(6), RELEASE SOFTWARE (fc3)
  

  The next example shows a product running IOS release 12.3(11)T3 with an image name of C3845-ADVIPSERVICESK9-M:

  Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.3(11)T3, RELEASE SOFTWARE (fc4)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2005 by Cisco Systems, Inc.
  

  Additional information about Cisco IOS release naming can be found at http://www.cisco.com/web/about/security/intelligence/ios-ref.html.

  Products Confirmed Not Vulnerable

  Cisco IOS XR is not affected.

  
  

  No other Cisco products are currently known to be affected by these vulnerabilities.

Details

• This section provides detailed information about these vulnerabilities.

  Overview

  Cisco IOS may be susceptible to remote code execution through attack vectors such as specific heap-based overflows in which internal operating system timers may execute arbitrary code from portions of memory that have been overwritten via exploitation.

  In many cases, a heap-based overflow in Cisco IOS will simply corrupt system memory and trigger a system reload when detected by the "Check Heaps" process, which constantly monitors for such memory corruption. In a successful attack against an appropriate heap-based overflow, it is possible to achieve code execution without the device crashing immediately.

  Cisco has devised counter-measures by implementing extra checks to enforce the proper integrity of system timers. This extra validation should reduce the possibility of heap-based overflow attack vectors achieving remote code execution.

  These improvements have been documented in Cisco Bug ID CSCei61732. ( registered customers only) .

  Background Information Regarding Heap Overflows

  As this security advisory pertains to heap overflows, the following additional information is provided to aid in understanding the terminology used in this advisory.

  RFC 2828 defines a vulnerability as "A flaw or weakness in a system's design, implementation, or operation and management that could be exploited to violate the system's security policy." The threat from any particular vulnerability in a system or a protocol depends on the ease and likelihood in which the normal operations of a system can be disrupted or compromised. In order to minimize the threat, each possible attack vector for a particular vulnerability should either be mitigated with protections which may prevent the circumstances required for exploitation or remediated with software that no longer contains the vulnerability.

  Many forms of malicious software, commonly known as "exploits", contain a payload that seeks to disrupt or compromise a system delivered through well-known attack vectors for particular vulnerabilities. In cases where it is likely that unpatched vulnerable systems exist, counter-measures are often employed to attempt to block any and all attack vectors to minimize the threat of successful exploitation. One popular attack method often found in the payload of exploits is known as a buffer overflow.

  A heap-based overflow is a type of buffer overflow against a data structure residing within the memory heap. The memory heap is a section of system memory used by the operating system of the device to satisfy the dynamic data storage requirements for currently running processes. In a successful heap-based overflow, the operating system fails to enforce bounds checking on a buffer, thus allowing for the possibility of overwriting adjacent locations in system memory.

  The threat from buffer overflows, like the one described in this advisory, may be remediated in multiple ways. One way is to remove the particular attack vector so that it no longer exists. Another way is to employ protections in the underlying system to minimize the consequences of any future buffer overflow vulnerabilities that may be discovered.

Workarounds

• There are no workarounds or configuration changes that will implement counter-measures equivalent to the increased integrity checks on system timers that have been introduced. In order to reduce the potential for system timer-related arbitrary code execution, an IOS upgrade is necessary.

  Successful exploitation requires an appropriate attack vector such as the vulnerability described in http://www.cisco.com/warp/publics/707/cisco-sa-20050729-ipv6.shtml. Vulnerability specific workarounds and mitigation steps may help to minimize the threat to the device by removing or minimizing the available attack vectors, but the device could still be vulnerable through any other attack vectors in which a software fix or mitigation has not been implemented.

  
  

Fixed Software

• When considering software upgrades, please also consult http://www.cisco.com/en/US/products/products_security_advisories_listing.html 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") for assistance.

  Each row of the Cisco IOS software table (below) describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild" and "Maintenance" columns. 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. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label).

  For further information on the terms "Rebuild" and "Maintenance," please consult the following URL: http://www.cisco.com/web/about/security/intelligence/ios-ref.html.

  Major Release	Availability of Repaired Releases
  Affected 12.0-Based Release	Rebuild	Maintenance
  12.0	12.0(28d)
  12.0DA	Vulnerable; migrate to 12.2(12)DA9 or later
  12.0DB	Vulnerable; migrate to 12.3(14)T4 or later
  12.0DC	Vulnerable; migrate to 12.2(15)BC2i or later
  12.0S	12.0(28)S5
  	12.0(30)S4
  	12.0(31)S1
  12.0SC	Vulnerable; migrate to 12.2(15)BC2i or later
  12.0SL	Vulnerable; migrate to 12.0(31)S1 or later
  12.0SP	Vulnerable; migrate to 12.0(31)S1 or later
  12.0ST	Vulnerable; migrate to 12.0(31)S1 or later
  12.0SX	Vulnerable; contact TAC
  12.0SZ	Vulnerable; migrate to 12.0(31)S1 or later
  12.0T	Vulnerable; migrate to 12.1(27b) or later
  12.0W5	12.0(25)W5-27d
  	12.0(28)W5-30b
  	12.0(28)W5-32a
  12.0WC	12.0(5)WC13
  12.0XA	Vulnerable; migrate to 12.1(27b) or later
  12.0XB	Vulnerable; migrate to 12.1(27b) or later
  12.0XC	Vulnerable; migrate to 12.1(27b) or later
  12.0XD	Vulnerable; migrate to 12.1(27b) or later
  12.0XE	Vulnerable; migrate to 12.1(26)E3 or later
  12.0XF	Vulnerable; migrate to 12.1(27b) or later
  12.0XG	Vulnerable; migrate to 12.1(27b) or later
  12.0XH	Vulnerable; migrate to 12.1(27b) or later
  12.0XI	Vulnerable; migrate to 12.1(27b) or later
  12.0XJ	Vulnerable; migrate to 12.1(27b) or later
  12.0XK	Vulnerable; migrate to 12.2(31) or later
  12.0XL	Vulnerable; migrate to 12.2(31) or later
  12.0XM	Vulnerable; migrate to 12.1(27b) or later
  12.0XN	Vulnerable; migrate to 12.1(27b) or later
  12.0XQ	Vulnerable; migrate to 12.1(27b) or later
  12.0XR	Vulnerable; migrate to 12.2(31) or later
  12.0XS	Vulnerable; migrate to 12.1(26)E3 or later
  12.0XV	Vulnerable; migrate to 12.1(27b) or later
  Affected 12.1-Based Release	Rebuild	Maintenance
  12.1	12.1(27b)
  12.1AA	Vulnerable; migrate to 12.2(31) or later
  12.1AX	Vulnerable; for c3750-ME, migrate to 12.2(25)EY3 or later. For c2970 and 3750, migrate to 12.2(25)SEB4, 12.2(25)SEC2, 12.2(25)SED or later.
  12.1AY	Vulnerable; migrate to 12.1(22)EA4a, 12.1(22)EA5a, 12.2(22)EA6 or later
  12.1AZ	Vulnerable; migrate to 12.1(22)EA4a, 12.1(22)EA5a, 12.2(22)EA6 or later
  12.1CX	Vulnerable; migrate to 12.2(31) or later
  12.1DA	Vulnerable; migrate to 12.2(12)DA9 or later
  12.1DB	Vulnerable; migrate to 12.3(14)T4 or later
  12.1DC	Vulnerable; migrate to 12.3(14)T4 or later
  12.1E	12.1(8b)E20
  	12.1(13)E17
  	12.1(23)E4
  	12.1(26)E3
  12.1EA	12.1(22)EA4a	12.1(22)EA6
  	12.1(22)EA5a
  12.1EB	12.1(26)EB1
  12.1EC	Vulnerable; migrate to 12.2(15)BC2i or later
  12.1EO	12.1(20)EO3, available 11/30/05
  12.1EU	Vulnerable; migrate to 12.2(20)EU2 or later
  12.1EV	Vulnerable; migrate to 12.2(26)SV1 or later
  12.1EW	12.1(12c)EW4
  	12.1(13)EW4
  	12.1(19)EW3
  	12.1(20)EW4
  12.1EX	Vulnerable; migrate to 12.1(26)E3 or later
  12.1EY	Vulnerable; migrate to 12.1(26)E3 or later
  12.1EZ	Vulnerable; migrate to 12.1(26)E3 or later
  12.1T	Vulnerable; migrate to 12.2(31) or later
  12.1XA	Vulnerable; migrate to 12.2(31) or later
  12.1XB	Vulnerable; migrate to 12.2(31) or later
  12.1XC	Vulnerable; migrate to 12.2(31) or later
  12.1XD	Vulnerable; migrate to 12.2(31) or later
  12.1XE	Vulnerable; migrate to 12.1(26)E3 or later
  12.1XF	Vulnerable; migrate to 12.3(16) or later
  12.1XG	Vulnerable; migrate to 12.3(16) or later
  12.1XH	Vulnerable; migrate to 12.2(31) or later
  12.1XI	Vulnerable; migrate to 12.2(31) or later
  12.1XJ	Vulnerable; migrate to 12.3(16) or later
  12.1XL	Vulnerable; migrate to 12.3(16) or later
  12.1XM	Vulnerable; migrate to 12.3(16) or later
  12.1XP	Vulnerable; migrate to 12.3(16) or later
  12.1XQ	Vulnerable; migrate to 12.3(16) or later
  12.1XR	Vulnerable; migrate to 12.3(16) or later
  12.1XS	Vulnerable; migrate to 12.2(31) or later
  12.1XT	Vulnerable; migrate to 12.3(16) or later
  12.1XU	Vulnerable; migrate to 12.3(16) or later
  12.1XV	Vulnerable; migrate to 12.3(16) or later
  12.1XW	Vulnerable; migrate to 12.2(31) or later
  12.1XX	Vulnerable; migrate to 12.2(31) or later
  12.1XY	Vulnerable; migrate to 12.2(31) or later
  12.1YA	Vulnerable; migrate to 12.3(16) or later
  12.1YB	Vulnerable; migrate to 12.3(16) or later
  12.1YC	Vulnerable; migrate to 12.3(16) or later
  12.1YD	Vulnerable; migrate to 12.3(16) or later
  12.1YE	Vulnerable; migrate to 12.3(16) or later
  12.1YF	Vulnerable; migrate to 12.3(16) or later
  12.1YH	Vulnerable; migrate to 12.3(16) or later
  12.1YI	Vulnerable; migrate to 12.3(16) or later
  12.1YJ	Vulnerable; migrate to 12.1(22)EA4a, 12.1(22)EA5a, 12.1(22)EA6 or later
  Affected 12.2-Based Release	Rebuild	Maintenance
  12.2	12.2(12m)
  	12.2(17f)
  	12.2(23f)
  	12.2(26b)
  	12.2(27b)
  	12.2(28c)
  	12.2(29a)	12.2(31)
  12.2B	Vulnerable; migrate to 12.3(14)T4 or later
  12.2BC	12.2(15)BC2i
  12.2BX	Vulnerable; migrate to 12.3(7)XI7, available 15-Nov-2005
  12.2BY	Vulnerable; migrate to 12.3(14)T4 or later
  12.2BZ	Vulnerable; migrate to 12.3(7)XI7, available 15-Nov-2005
  12.2CX	Vulnerable; migrate to 12.2(15)BC2i or later
  12.2CY	Vulnerable; migrate to 12.2(15)BC2i or later
  12.2CZ	12.2(15)CZ3, available 3-Nov-2005
  12.2DA	12.2(10)DA4
  	12.2(12)DA9
  12.2DD	Vulnerable; migrate to 12.3(14)T4 or later
  12.2DX	Vulnerable; migrate to 12.3(14)T4 or later
  12.2EU	12.2(20)EU2
  12.2EW	12.2(18)EW5
  	12.2(20)EW3
  12.2EWA	12.2(20)EWA3
  	12.2(25)EWA3
  12.2EX		12.2(25)EX, available 03-Nov-2005
  12.2EY	12.2(25)EY3	Migrate to 12.2(25)SED
  12.2EZ	Vulnerable; migrate to 12.2(25)SEC2, 12.2(25)SED or later
  12.2FX		12.2(25)FX, available 07-Nov-2005
  12.2FY		12.2(25)FY
  12.2JA	Vulnerable; migrate to 12.3(7)JA1 or later
  12.2JK	12.2(15)JK5
  12.2MB	12.2(4)MB13c
  12.2MC	12.2(15)MC2e
  12.2S	12.2(14)S15
  	12.2(18)S10
  	12.2(20)S9
  	12.2(25)S6
  	12.2(30)S1, available 14-Nov-2005
  12.2SBC		12.2(27)SBC
  12.2SE	12.2(25)SEB4	12.2(25)SED
  	12.2(25)SEC2
  12.2SG		12.2(25)SG
  12.2SO	12.2(18)SO4
  12.2SU	Vulnerable; migrate to 12.3(14)T4 or later
  12.2SV	12.2(26)SV1
  	12.2(27)SV1, available 15-Nov-2005
  12.2SW		12.2(25)SW4
  12.2SX	Vulnerable; migrate to 12.2(17d)SXB10 or later
  12.2SXA	Vulnerable; migrate to 12.2(17d)SXB10 or later
  12.2SXB	12.2(17d)SXB10
  12.2SXD	12.2(18)SXD6
  12.2SXE	12.2(18)SXE3
  12.2SXF		12.2(18)SXF
  12.2SY	Vulnerable; migrate to 12.2(17d)SXB10 or later
  12.2SZ	Vulnerable; migrate to 12.2(25)S6 or later
  12.2T	12.2(15)T17
  12.2TPC	12.2(8)TPC10a, available TBD
  12.2XA	Vulnerable; migrate to 12.3(16) or later
  12.2XB	Vulnerable; migrate to 12.3(16) or later
  12.2XC	Vulnerable; migrate to 12.3(14)T4 or later
  12.2XD	Vulnerable; migrate to 12.3(16) or later
  12.2XE	Vulnerable; migrate to 12.3(16) or later
  12.2XF	Vulnerable; migrate to 12.2(15)BC2i or later
  12.2XG	Vulnerable; migrate to 12.3(16) or later
  12.2XH	Vulnerable; migrate to 12.3(16) or later
  12.2XI	Vulnerable; migrate to 12.3(16) or later
  12.2XJ	Vulnerable; migrate to 12.3(16) or later
  12.2XK	Vulnerable; migrate to 12.3(16) or later
  12.2XL	Vulnerable; migrate to 12.3(16) or later
  12.2XM	Vulnerable; migrate to 12.3(16) or later
  12.2XN	Vulnerable; migrate to 12.3(16) or later
  12.2XQ	Vulnerable; migrate to 12.3(16) or later
  12.2XR	12.2(2)XR and 12.2(4)XR vulnerable, migrate to 12.3(16) or later
  	12.2(15)XR vulnerable; migrate to 12.3(7)JA1
  12.2XS	Vulnerable; migrate to 12.3(16) or later
  12.2XT	Vulnerable; migrate to 12.3(16) or later
  12.2XU	Vulnerable; migrate to 12.3(16) or later
  12.2XV	Vulnerable; migrate to 12.3(16) or later
  12.2XW	Vulnerable; migrate to 12.3(16) or later
  12.2YA	12.2(4)YA11, available TBD
  12.2YB	Vulnerable; migrate to 12.3(16) or later
  12.2YC	Vulnerable; migrate to 12.3(16) or later
  12.2YD	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YE	Vulnerable; migrate to 12.2(25)S6 or later
  12.2YF	Vulnerable; migrate to 12.3(16) or later
  12.2YG	Vulnerable; migrate to 12.3(16) or later
  12.2YH	Vulnerable; migrate to 12.3(16) or later
  12.2YJ	Vulnerable; migrate to 12.3(16) or later
  12.2YK	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YL	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YM	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YN	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YO	Vulnerable; migrate to 12.2(17d)SXB10 or later
  12.2YP	Vulnerable; migrate to 12.3(16) or later
  12.2YQ	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YR	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YS		12.2(15)YS
  12.2YT	Vulnerable; migrate to 12.3(16) or later
  12.2YU	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YV	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YW	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YX	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YY	Vulnerable; migrate to 12.3(14)T4 or later
  12.2YZ	Vulnerable; migrate to 12.2(25)S6 or later
  12.2ZA	Vulnerable; migrate to 12.2(17d)SXB10 or later
  12.2ZB	Vulnerable; migrate to 12.3(14)T4 or later
  12.2ZC	Vulnerable; migrate to 12.3(14)T4 or later
  12.2ZD	12.2(13)ZD4
  12.2ZE	Vulnerable; migrate to 12.3(16) or later
  12.2ZF	Vulnerable; migrate to 12.3(14)T4 or later
  12.2ZG	Vulnerable; migrate to 12.3(8)YG3 or later for SOHO9x migrate to 12.3(2)XA5 or later for c83x
  12.2ZH	12.2(13)ZH8, available TBD
  12.2ZJ	Vulnerable; migrate to 12.3(14)T4 or later
  12.2ZL	Vulnerable; migrate to 12.3(4)XK4 or later for c17xx migrate to 12.4(3a) or later for c3200 migrate to 12.3(7)XR6 or later for ICS7750
  12.2ZN	Vulnerable; migrate to 12.3(14)T4 or later
  12.2ZP	Vulnerable; migrate to 12.3(14)T4 or later
  Affected 12.3-Based Release	Rebuild	Maintenance
  12.3	12.3(3i)
  	12.3(5f)
  	12.3(6f)
  	12.3(9e)
  	12.3(10e)
  	12.3(12e)
  	12.3(13b)
  	12.3(15b)	12.3(16)
  12.3B	Vulnerable; migrate to 12.3(14)T4 or later
  12.3BC	12.3(9a)BC7
  	12.3(13a)BC1
  12.3BW	Vulnerable; migrate to 12.3(14)T4 or later
  12.3JA	12.3(2)JA5
  	12.3(4)JA1
  	12.3(7)JA1
  12.3JK	12.3(2)JK1
  12.3JX	12.3(7)JX
  12.3T	12.3(7)T12
  	12.3(8)T11
  	12.3(11)T8
  	12.3(14)T4
  12.3TPC	12.3(4)TPC11a
  12.3XA	12.3(2)XA5, available TBD
  12.3XB	Vulnerable; migrate to 12.3(14)T4 or later
  12.3XC	12.3(2)XC4
  12.3XD	Vulnerable; migrate to 12.3(14)T4 or later
  12.3XE	12.3(4)XE4, available TBD
  12.3XF	Vulnerable; migrate to 12.3(14)T4 or later
  12.3XG	12.3(4)XG5
  12.3XH	Vulnerable; migrate to 12.3(14)T4 or later
  12.3XI	12.3(7)XI7, available 15-Nov-2005
  12.3XJ	Vulnerable; migrate to 12.3(11)YF4 or later
  12.3XK	12.3(4)XK4
  12.3XM	Vulnerable; migrate to 12.3(14)T4 or later
  12.3XQ	Vulnerable; migrate to 12.4(3a) or later
  12.3XR	12.3(7)XR6
  12.3XS	Vulnerable; migrate to 12.4(3a) or later
  12.3XU	Vulnerable; migrate to 12.4(2)T1 or later
  12.3XW	Vulnerable; migrate to 12.3(11)YF4 or later
  12.3XX	Vulnerable; migrate to 12.4(3a) or later
  12.3XY	Vulnerable; migrate to 12.3(14)T4 or later
  12.3YA	Vulnerable; migrate to 12.4(3a) or later for C828; migrate to 12.3(8)YG3 or later for SOHO9x, C83x
  12.3YD	Vulnerable; migrate to 12.4(2)T1 or later
  12.3YF	12.3(11)YF4
  12.3YG	12.3(8)YG3
  12.3YH	Vulnerable; migrate to 12.3(8)YI3 or later
  12.3YI	12.3(8)YI3
  12.3YJ	12.3(14)YQ3
  12.3YK	12.3(11)YK2
  12.3YQ	12.3(14)YQ3
  12.3YS	12.3(11)YS1
  12.3YT	12.3(14)YT1
  12.3YU	12.3(14)YU1
  Affected 12.4-Based Release	Rebuild	Maintenance
  12.4	12.4(1b)
  	12.4(3a)	12.4(5)
  12.4MR		12.4(2)MR1
  12.4T	12.4(2)T1	12.4(4)T
  12.4XA		12.4(2)XA
  12.4XB		12.4(2)XB, available 18-Nov-2005

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of malicious use of the vulnerability described in this advisory. Exploit code exists for this vulnerability. It was used in a demonstration by Mike Lynn on July 27, 2005 at the Black Hat USA 2005 security conference where a heap overflow via an IPv6 attack vector achieved remote code execution. The IPv6 attack vector was addressed separately in a Cisco security advisory released on July 29, 2005.

  
  

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20051102-timers

Revision History

• Revision 1.2	4-Nov-2005	Further clarified obtaining fixed software section, updated fixed software for 12.2EWA, 12.2SW, 12.4, 12.4T
  Revision 1.1	3-Nov-2005	Clarified obtaining fixed software section
  Revision 1.0	2-Nov-2005	Initial public release

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