[apops] Cisco Security Advisory: Cisco IOS SSL VPN Vulnerability

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  • Subject: [apops] Cisco Security Advisory: Cisco IOS SSL VPN Vulnerability
  • From: Cisco Systems Product Security Incident Response Team <psirt at cisco dot com>
  • Date: Wed, 22 Sep 2010 18:00:00 +0200
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      Cisco IOS SSL VPN Vulnerability
      
      Advisory ID: cisco-sa-20100922-sslvpn
      
      http://www.cisco.com/warp/public/707/cisco-sa-20100922-sslvpn.shtml
      
      Revision 1.0
      
      For Public Release 2010 September 22 1600 UTC (GMT)
      
      - ---------------------------------------------------------------------
      
      Summary
      =======
      
      Cisco IOS  Software contains a vulnerability when the Cisco IOS SSL
      VPN feature is configured with an HTTP redirect. Exploitation could
      allow a remote, unauthenticated user to cause a memory leak on the
      affected devices, that could result in a memory exhaustion condition
      that may cause device reloads, the inability to service new TCP
      connections, and other denial of service (DoS) conditions.
      
      Cisco has released free software updates that address this
      vulnerability. There is a workaround to mitigate this vulnerability.
      
      This advisory is posted at 
      http://www.cisco.com/warp/public/707/cisco-sa-20100922-sslvpn.shtml
      
      Note: The September 22, 2010, Cisco IOS Software Security Advisory
      bundled publication includes six Cisco Security Advisories. Five of
      the advisories address vulnerabilities in Cisco IOS Software, and one
      advisory addresses vulnerabilities in Cisco Unified Communications
      Manager. Each advisory lists the releases that correct the
      vulnerability or vulnerabilities detailed in the advisory. The table
      at the following URL lists releases that correct all Cisco IOS
      Software vulnerabilities that have been published on September 22,
      2010, or earlier:
      
      http://www.cisco.com/warp/public/707/cisco-sa-20100922-bundle.shtml
      
      Individual publication links are in "Cisco Event Response: Semiannual
      Cisco IOS Software Security Advisory Bundled Publication" at the
      following link:
      
      http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_sep10.html
      
      Affected Products
      =================
      
      Vulnerable Products
      +------------------
      
      Devices running affected versions of Cisco IOS Software are
      vulnerable if configured with SSL VPN and HTTP port redirection.
      
      The following methods may be used to confirm if the device is
      configured for Cisco IOS SSL VPNs and is vulnerable:
      
      If the output from show running-config | include webvpn contains
      "webvpn gateway <word>" then the device is supporting the Cisco IOS
      SSL VPN feature. A device is vulnerable if it has the inservice
      command in at least one of the "webvpn gateway" sections and is
      configured for HTTP port redirection. The following example shows a
      vulnerable device configured with Cisco IOS SSL VPN:
      
          Router#show running | section webvpn
          webvpn gateway Gateway
           ip address 10.1.1.1 port 443
           http-redirect port 80
           ssl trustpoint Gateway-TP
           inservice
           !
          Router#
      
      A device that supports the Cisco IOS SSL VPN is not vulnerable if
      "webvpn gateway" is not configured.
      
      To determine the Cisco IOS Software release that is running on a
      Cisco product, administrators can log in to the device and issue the
      show version command to display the system banner. The system banner
      confirms that the device is running Cisco IOS Software by displaying
      text similar to "Cisco Internetwork Operating System Software" or
      "Cisco IOS Software." The image name displays in parentheses,
      followed by "Version" and the Cisco IOS Software release name. Other
      Cisco devices do not have the show version command or may provide
      different output.
      
      The following example identifies a Cisco product that is running
      Cisco IOS Software Release 12.4(20)T with an installed image name of
      C2800NM-ADVSECURITYK9-M:
      
          Router#show version
          Cisco IOS Software, 2800 Software (C2800NM-ADVSECURITYK9-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 22:00 by prod_rel_team
      
          ! --- output truncated
      
      Additional information about Cisco IOS Software release naming
      conventions is available in "White Paper: Cisco IOS Reference Guide"
      at the following link: http://www.cisco.com/warp/public/620/1.html
      
      Products Confirmed Not Vulnerable
      +--------------------------------
      
      The following products are not affected by this vulnerability:
      
        * Cisco ASA 5500 Series Adaptive Security Appliances
        * Cisco IOS XR Software
        * Cisco IOS XE Software
      
      No other Cisco products are currently known to be affected by this
      vulnerability.
      
      Details
      =======
      
      The Cisco IOS SSL VPN feature provides remote access to enterprise
      sites to users anywhere on the Internet. The SSL VPN provides users
      with secure access to specific enterprise applications, such as
      e-mail and web browsing, without requiring them to have VPN client
      software installed on their end-user devices.
      
      Further information about Cisco IOS SSL VPN is available in the
      "Cisco IOS Software Release 12.4T SSL VPN feature guide" at the
      following link: 
      http://www.cisco.com/en/US/docs/ios/12_4t/12_4t11/htwebvpn.html leavingcisco.com
      
      A device configured for SSL VPN with HTTP port redirection may leak
      transmission control blocks (TCBs) when processing an abnormally
      disconnected SSL session. Continued exploitation may cause the device
      to deplete memory resources, which could result in device reloads,
      the inability to service new TCP connections, and other DoS
      conditions. Authentication is not required to exploit this
      vulnerability.
      
      A complete TCP 3-way handshake is required to exploit this
      vulnerability. The memory leak can be detected by running the command
      show tcp brief as shown in the following example:
      
          Router#show tcp brief
          TCB       Local Address      Foreign Address     (state)
          468BBDC0  192.168.0.22.80   192.168.0.33.19794   CLOSEWAIT
          482D4730  192.168.0.22.80   192.168.0.33.22092   CLOSEWAIT
          482779A4  192.168.0.22.80   192.168.0.33.16978   CLOSEWAIT
          4693DEBC  192.168.0.22.80   192.168.0.33.21580   CLOSEWAIT
          482D3418  192.168.0.22.80   192.168.0.33.17244   CLOSEWAIT
          482B8ACC  192.168.0.22.80   192.168.0.33.16564   CLOSEWAIT
          46954EB0  192.168.0.22.80   192.168.0.33.19532   CLOSEWAIT
          468BA9B8  192.168.0.22.80   192.168.0.33.15781   CLOSEWAIT
          482908C4  192.168.0.22.80   192.168.0.33.19275   CLOSEWAIT
          4829D66C  192.168.0.22.80   192.168.0.33.19314   CLOSEWAIT
          468A2D94  192.168.0.22.80   192.168.0.33.14736   CLOSEWAIT
          4688F590  192.168.0.22.80   192.168.0.33.18786   CLOSEWAIT
          4693CBA4  192.168.0.22.80   192.168.0.33.12176   CLOSEWAIT
          4829ABC4  192.168.0.22.80   192.168.0.33.39629   CLOSEWAIT
          4691206C  192.168.0.22.80   192.168.0.33.17818   CLOSEWAIT
          46868224  192.168.0.22.80   192.168.0.33.16774   CLOSEWAIT
          4832BFAC  192.168.0.22.80   192.168.0.33.39883   CLOSEWAIT
          482D10CC  192.168.0.22.80   192.168.0.33.13677   CLOSEWAIT
          4829B120  192.168.0.22.80   192.168.0.33.20870   CLOSEWAIT
          482862FC  192.168.0.22.80   192.168.0.33.17035   CLOSEWAIT
          482EC13C  192.168.0.22.80   192.168.0.33.16053   CLOSEWAIT
          482901D8  192.168.0.22.80   192.168.0.33.16200   CLOSEWAIT
      
      In the output above, the Transmission Control Blocks (TCBs) in the
      state CLOSEWAIT will not transition and represent a memory leak. Note
      that only TCP connections with a local TCP port of 80 (the well-known
      port for HTTP), as evidenced in the above example by a Local Address
      of 192.168.0.22.80, are relevant.
      
      This vulnerability is documented in Cisco bug ID CSCtg21685 
      and Common Vulnerabilities and Exposures (CVE) identifier 
      CVE-2010-2836 has been assigned to this vulnerability.
      
      Vulnerability Scoring Details
      =============================
      
      Cisco has provided scores for the vulnerability in this advisory
      based on the Common Vulnerability Scoring System (CVSS). The CVSS
      scoring in this Security Advisory is done in accordance with CVSS
      version 2.0.
      
      CVSS is a standards-based scoring method that conveys vulnerability
      severity and helps determine urgency and priority of response.
      
      Cisco has provided a base and temporal score. Customers can then
      compute environmental scores to assist in determining the impact of
      the vulnerability in individual networks.
      
      Cisco has provided an FAQ to answer additional questions regarding
      CVSS at
      
      http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html
      
      Cisco has also provided a CVSS calculator to help compute the
      environmental impact for individual networks at
      
      http://intellishield.cisco.com/security/alertmanager/cvss
      
      CSCtg21685 - SSLVPN : TCP remains stuck in closewait state
      
      CVSS Base Score - 7.8
      Access Vector           Network
      Access Complexity       Low
      Authentication          None
      Confidentiality Impact  None
      Integrity Impact        None
      Availability Impact     Complete
      
      CVSS Temporal Score - 6.4
      Exploitability          Functional
      Remediation Level       Official Fix
      Report Confidence       Confirmed
      
      Impact
      ======
      
      Successful exploitation of the vulnerability may result in a lack of
      available memory resources on the affected device, which could affect
      new connections to the device such as SSH and Telnet connections.
      Depletion of memory resources may also result in failing of routing
      protocols and other services.
      
      Software Versions and Fixes
      ===========================
      
      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 following Cisco IOS Software table corresponds to a
      Cisco IOS Software train. If a particular train is vulnerable, the
      earliest releases that contain the fix are listed in the First Fixed
      Release For This Advisory column. The First Fixed Release for All
      Advisories in the September 2010 Bundle Publication column lists the
      earliest possible releases that correct all the published
      vulnerabilities in the Cisco IOS Software Security Advisory bundled
      publication. Cisco recommends upgrading to the latest available
      release, where possible.
      
      +-------------------------------------------------------------------+
      |   Major    |             Availability of Repaired Releases        |
      |  Release   |                                                      |
      |------------+------------------------------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 12.0-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |-------------------------------------------------------------------|
      | There are no affected 12.0 based releases                         |
      |-------------------------------------------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 12.1-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |-------------------------------------------------------------------|
      | There are no affected 12.1 based releases                         |
      |-------------------------------------------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 12.2-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |-------------------------------------------------------------------|
      | There are no affected 12.2 based releases                         |
      |-------------------------------------------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 12.3-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |-------------------------------------------------------------------|
      | There are no affected 12.3 based releases                         |
      |-------------------------------------------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 12.4-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |------------+----------------------+-------------------------------|
      | 12.4       | Not Vulnerable       | 12.4(25d)                     |
      |------------+----------------------+-------------------------------|
      | 12.4GC     | Not Vulnerable       | 12.4(24)GC2                   |
      |------------+----------------------+-------------------------------|
      | 12.4JA     | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JDA    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JDC    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JDD    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JHA    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JHB    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JK     | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JL     | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JMA    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JMB    | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JX     | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4JY     | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      | 12.4MD     | Not Vulnerable       | 12.4(24)MD2                   |
      |------------+----------------------+-------------------------------|
      |            |                      | 12.4(22)MDA4                  |
      | 12.4MDA    | Not Vulnerable       |                               |
      |            |                      | 12.4(24)MDA1                  |
      |------------+----------------------+-------------------------------|
      | 12.4MR     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4MRA                       |
      |------------+----------------------+-------------------------------|
      | 12.4MRA    | Not Vulnerable       | 12.4(20)MRA1                  |
      |------------+----------------------+-------------------------------|
      | 12.4SW     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      |            | Releases Prior to    |                               |
      |            | 12.4(15)T13 are not  |                               |
      |            | vulnerable. First    |                               |
      |            | fixed 12.4(15)T14    |                               |
      |            |                      | 12.4(15)T14                   |
      |            | Releases Prior to    |                               |
      | 12.4T      | 12.4(20)T5 are not   | 12.4(20)T6                    |
      |            | vulnerable. First    |                               |
      |            | fixed 12.4(20)T6     | 12.4(24)T4                    |
      |            |                      |                               |
      |            | Releases Prior to    |                               |
      |            | 12.4(24)T2 are not   |                               |
      |            | vulnerable. First    |                               |
      |            | fixed 12.4(24)T4     |                               |
      |------------+----------------------+-------------------------------|
      | 12.4XA     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XB     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XC     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XD     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      |            |                      | Releases prior to 12.4(6)XE5  |
      |            |                      | are vulnerable, release 12.4  |
      | 12.4XE     | Not Vulnerable       | (6)XE5 and later are not      |
      |            |                      | vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XF     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XG     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XJ     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XK     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      |            |                      | Vulnerable; Contact your      |
      |            |                      | support organization per the  |
      | 12.4XL     | Not Vulnerable       | instructions in Obtaining     |
      |            |                      | Fixed Software section of     |
      |            |                      | this advisory                 |
      |------------+----------------------+-------------------------------|
      | 12.4XM     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      |            |                      | Vulnerable; Contact your      |
      |            |                      | support organization per the  |
      | 12.4XN     | Not Vulnerable       | instructions in Obtaining     |
      |            |                      | Fixed Software section of     |
      |            |                      | this advisory                 |
      |------------+----------------------+-------------------------------|
      |            |                      | Vulnerable; Contact your      |
      |            |                      | support organization per the  |
      | 12.4XP     | Not Vulnerable       | instructions in Obtaining     |
      |            |                      | Fixed Software section of     |
      |            |                      | this advisory                 |
      |------------+----------------------+-------------------------------|
      | 12.4XQ     | Not Vulnerable       | 12.4(15)XQ6; Available on     |
      |            |                      | 22-SEP-10                     |
      |------------+----------------------+-------------------------------|
      |            |                      | 12.4(15)XR9                   |
      | 12.4XR     | Not Vulnerable       |                               |
      |            |                      | 12.4(22)XR7                   |
      |------------+----------------------+-------------------------------|
      | 12.4XT     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      |            |                      | Vulnerable; Contact your      |
      |            |                      | support organization per the  |
      | 12.4XV     | Not Vulnerable       | instructions in Obtaining     |
      |            |                      | Fixed Software section of     |
      |            |                      | this advisory                 |
      |------------+----------------------+-------------------------------|
      | 12.4XW     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XY     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4XZ     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      | 12.4YA     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 12.4T                         |
      |------------+----------------------+-------------------------------|
      |            |                      | Vulnerable; Contact your      |
      |            |                      | support organization per the  |
      | 12.4YB     | Not Vulnerable       | instructions in Obtaining     |
      |            |                      | Fixed Software section of     |
      |            |                      | this advisory                 |
      |------------+----------------------+-------------------------------|
      |            |                      | Vulnerable; Contact your      |
      |            |                      | support organization per the  |
      | 12.4YD     | Not Vulnerable       | instructions in Obtaining     |
      |            |                      | Fixed Software section of     |
      |            |                      | this advisory                 |
      |------------+----------------------+-------------------------------|
      | 12.4YE     | Not Vulnerable       | 12.4(24)YE1                   |
      |------------+----------------------+-------------------------------|
      | 12.4YG     | Not Vulnerable       | 12.4(24)YG3                   |
      |------------+----------------------+-------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 15.0-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |------------+----------------------+-------------------------------|
      | 15.0M      | 15.0(1)M3            | 15.0(1)M3                     |
      |------------+----------------------+-------------------------------|
      |            | Cisco 7600 and 10000 | Cisco 7600 and 10000 Series   |
      |            | Series routers: Not  | routers: 15.0(1)S1 (available |
      |            | vulnerable           | early October 2010)           |
      | 15.0S      |                      |                               |
      |            | Please see Cisco     | Please see Cisco IOS-XE       |
      |            | IOS-XE Software      | Software Availability         |
      |            | Availability         |                               |
      |------------+----------------------+-------------------------------|
      | 15.0XA     | Not Vulnerable       | Vulnerable; first fixed in    |
      |            |                      | 15.1T                         |
      |------------+----------------------+-------------------------------|
      | 15.0XO     | Not Vulnerable       | Not Vulnerable                |
      |------------+----------------------+-------------------------------|
      |  Affected  | First Fixed Release  |  First Fixed Release for All  |
      | 15.1-Based |  for This Advisory   |  Advisories in the September  |
      |  Releases  |                      |    2010 Bundle Publication    |
      |------------+----------------------+-------------------------------|
      |            | 15.1(1)T1            |                               |
      | 15.1T      |                      | 15.1(2)T1                     |
      |            | 15.1(2)T0a           |                               |
      |------------+----------------------+-------------------------------|
      |            | Vulnerability        | Vulnerable; first fixed in    |
      | 15.1XB     | limited to 15.1(1)   | 15.1T                         |
      |            | XB1.                 |                               |
      +-------------------------------------------------------------------+
      
      Cisco IOS XE Software
      +--------------------
      
      +-------------------------------------------------------------------+
      | Cisco IOS |   First Fixed    |    First Fixed Release for All     |
      |    XE     | Release for This |  Advisories in the September 2010  |
      |  Release  |     Advisory     |         Bundle Publication         |
      |-----------+------------------+------------------------------------|
      | 2.1.x     | Not Vulnerable   | Not Vulnerable                     |
      |-----------+------------------+------------------------------------|
      | 2.2.x     | Not Vulnerable   | Not Vulnerable                     |
      |-----------+------------------+------------------------------------|
      | 2.3.x     | Not Vulnerable   | Not Vulnerable                     |
      |-----------+------------------+------------------------------------|
      | 2.4.x     | Not Vulnerable   | Not Vulnerable                     |
      |-----------+------------------+------------------------------------|
      | 2.5.x     | Not Vulnerable   | Vulnerable; migrate to 2.6.2 or    |
      |           |                  | later                              |
      |-----------+------------------+------------------------------------|
      | 2.6.x     | Not Vulnerable   | 2.6.2                              |
      |-----------+------------------+------------------------------------|
      | 3.1.xS    | Not Vulnerable   | Not Vulnerable                     |
      +-------------------------------------------------------------------+
      
      For mapping of Cisco IOS XE Software to Cisco IOS Software releases,
      please refer to the Cisco IOS XE 2 and Cisco IOS XE 3S Release Notes.
      
      Cisco IOS XR System Software
      +---------------------------
      
      Cisco IOS XR Software is not affected by the vulnerabilities
      disclosed in the September 22, 2010, Cisco IOS Software Security
      Advisory bundled publication.
      
      Workarounds
      ===========
      
      Disabling HTTP redirection for SSL VPN connections can be used as a
      workaround for this vulnerability. HTTP redirection for SSL VPN
      connections is disabled by executing the command no http-redirect
      port in webvpn gateway configuration mode.
      
      In addition, manually clearing the hung TCBs with the command clear
      tcp tcb * will transition the TCBs into a CLOSED state. After a time
      they will clear the CLOSED state and the memory will be released.
      
      Note:  Clearing the TCB will clear both legitimate and hung
      connections, including remote connections to the device such as
      Telnet and SSH connections.
      
      The Cisco Applied Mitigation Bulletin (AMB) "Identifying and
      Mitigating Exploitation of the TCP State Manipulation Denial of
      Service Vulnerabilities in Multiple Cisco Products", available at
      http://www.cisco.com/warp/public/707/cisco-amb-20090908-tcp24.shtml,
      contains two mitigations (EEM scripts and SNMP) that can be used to
      detect and clear hung TCP connections.
      
      Embedded Event Manager (EEM)
      +---------------------------
      
      A Cisco IOS Embedded Event Manager (EEM) policy that is based on Tool
      Command Language (Tcl) can be used on vulnerable Cisco IOS devices to
      identify and detect a hung, extended, or indefinite TCP connection
      that is caused by this vulnerability. The policy allows
      administrators to monitor TCP connections on a Cisco IOS device. When
      Cisco IOS EEM detects potential exploitation of this vulnerability,
      the policy can trigger a response by sending a syslog message or a
      Simple Network Management Protocol (SNMP) trap to clear the TCP
      connection. The example policy provided in this document is based on
      a Tcl script that monitors and parses the output from two commands at
      defined intervals, produces a syslog message when the monitor
      threshold reaches its configured value, and can reset the TCP
      connection.
      
      The Tcl script is available for download at the "Cisco Beyond:
      Embedded Event Manager (EEM) Scripting Community" at the following
      link: http://forums.cisco.com/eforum/servlet/EEM?page=eem&fn=script&scriptId=2041
      A sample device configuration is provided below.
      
      
              !
              !-- Location where the Tcl script will be stored
              !
      
              event manager directory user policy disk0:/eem
      
              !
              !-- Define variable and set the monitoring interval
              !-- as an integer (expressed in seconds)
              !
      
              event manager environment EEM_MONITOR_INTERVAL 60
      
              !
              !-- Define variable and set the threshold value as
              !-- an integer for the number of retransmissions
              !-- that determine if the TCP connection is hung
              !-- (a recommended value to use is 15)
              !
      
              event manager environment EEM_MONITOR_THRESHOLD 15
      
              !
              !-- Define variable and set the value to "yes" to
              !-- enable the clearing of hung TCP connections
              !
      
              event manager environment EEM_MONITOR_CLEAR yes
      
              !
              !-- Define variable and set to the TCP connection
              !-- state or states that script will monitor, which
              !-- can be a single state or a space-separated list
              !-- of states
              !
      
              event manager environment EEM_MONITOR_STATES CLOSEWAIT
      
              !
              !-- Register the script as a Cisco EEM policy
              !
      
              event manager policy monitor-sockets.tcl
      
              !
      
      For more details, refer to the sections "EEM Detecting And Clearing
      Hung TCP Connection" and "Identification: Detecting and Clearing Hung
      TCP Connection Using SNMP" of this AMB at the following link: 
      http://www.cisco.com/warp/public/707/cisco-amb-20090908-tcp24.shtml
      
      Obtaining Fixed Software
      ========================
      
      Cisco has released free software updates that address these
      vulnerabilities. Prior to deploying software, customers should
      consult their maintenance provider or check the software for feature
      set compatibility and known issues specific to their environment.
      
      Customers may only install and expect support for the feature sets
      they have purchased. By installing, downloading, accessing or
      otherwise using such software upgrades, customers agree to be bound
      by the terms of Cisco's software license terms found at 
      http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html
      or as otherwise set forth at Cisco.com Downloads at 
      http://www.cisco.com/public/sw-center/sw-usingswc.shtml
      
      Do not contact psirt at cisco dot com or security-alert at cisco dot com for
      software upgrades.
      
      Customers with Service Contracts
      +-------------------------------
      
      Customers with contracts should obtain upgraded software through
      their regular update channels. For most customers, this means that
      upgrades should be obtained through the Software Center on Cisco's
      worldwide website at http://www.cisco.com
      
      Customers using Third Party Support Organizations
      +------------------------------------------------
      
      Customers whose Cisco products are provided or maintained through
      prior or existing agreements with third-party support organizations,
      such as Cisco Partners, authorized resellers, or service providers
      should contact that support organization for guidance and assistance
      with the appropriate course of action in regards to this advisory.
      
      The effectiveness of any workaround or fix is dependent on specific
      customer situations, such as product mix, network topology, traffic
      behavior, and organizational mission. Due to the variety of affected
      products and releases, customers should consult with their service
      provider or support organization to ensure any applied workaround or
      fix is the most appropriate for use in the intended network before it
      is deployed.
      
      Customers without Service Contracts
      +----------------------------------
      
      Customers who purchase direct from Cisco but do not hold a Cisco
      service contract, and customers who purchase through third-party
      vendors but are unsuccessful in obtaining fixed software through
      their point of sale should acquire upgrades by contacting the Cisco
      Technical Assistance Center (TAC). TAC contacts are as follows.
      
        * +1 800 553 2447 (toll free from within North America)
        * +1 408 526 7209 (toll call from anywhere in the world)
        * e-mail: tac at cisco dot com
      
      Customers should have their product serial number available and be
      prepared to give the URL of this notice as evidence of entitlement to
      a free upgrade. Free upgrades for non-contract customers must be
      requested through the TAC.
      
      Refer to 
      http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html
      for additional TAC contact information, including localized telephone 
      numbers, and instructions and e-mail addresses for use in various 
      languages.
      
      Exploitation and Public Announcements
      =====================================
      
      The Cisco PSIRT is not aware of any public announcements or malicious
      use of the vulnerability described in this advisory.
      
      This vulnerability was found during the troubleshooting of a customer
      service request.
      
      Status of this Notice: FINAL
      ============================
      
      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.
      
      A stand-alone copy or Paraphrase of the text of this document that
      omits the distribution URL in the following section is an
      uncontrolled copy, and may lack important information or contain
      factual errors.
      
      Distribution
      ============
      
      This advisory is posted on Cisco's worldwide website at :
      
      http://www.cisco.com/warp/public/707/cisco-sa-20100922-sslvpn.shtml
      
      In addition to worldwide web posting, a text version of this notice
      is clear-signed with the Cisco PSIRT PGP key and is posted to the
      following e-mail and Usenet news recipients.
      
        * cust-security-announce at cisco dot com
        * first-bulletins at lists dot first dot org
        * bugtraq at securityfocus dot com
        * vulnwatch at vulnwatch dot org
        * cisco at spot dot colorado dot edu
        * cisco-nsp at puck dot nether dot net
        * full-disclosure at lists.grok dot org dot uk
        * comp.dcom.sys.cisco at newsgate dot cisco dot com
      
      Future updates of this advisory, if any, will be placed on Cisco's
      worldwide website, but may or may not be actively announced on
      mailing lists or newsgroups. Users concerned about this problem are
      encouraged to check the above URL for any updates.
      
      Revision History
      ================
      
      +-----------------------------------------+
      | Revision |                   | Initial  |
      | 1.0      | 2010-September-22 | public   |
      |          |                   | release. |
      +-----------------------------------------+
      
      Cisco Security Procedures
      =========================
      
      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 
      http://www.cisco.com/en/US/products/products_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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