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Cisco Security Advisory: Multiple Vulnerabilities in CiscoSecure ACS for Windows NT Server
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Thu, 21 Sep 2000 11:00:00 -0400


   Cisco Security Advisory: Multiple Vulnerabilities in CiscoSecure ACS for
                               Windows NT Server

Revision 1.2

  For Public Release 2000 September 21 16:00 (GMT+0100)


   Multiple vulnerabilities have been identified and fixed in CiscoSecure
   ACS for Windows NT Server:
     * The CSAdmin software module can be forced to crash by sending it
       an oversized URL. This defect is documented as Cisco bug ID
     * CiscoSecure ACS for Windows NT Server can be placed into an
       unstable state by sending it an oversized TACACS+ packet. This
       defect is documented as Cisco bug ID CSCdr51286.
     * The enable password can be bypassed to gain unauthorized
       privileges on a router or switch when CiscoSecure ACS for Windows
       NT Server is used in conjunction with an LDAP server that allows
       users to have null passwords. This defect is documented as Cisco
       bug ID CSCdr26113.

   All releases of CiscoSecure ACS for Windows NT Server up to and
   including 2.1(x), 2.3(3), and 2.4(2) are vulnerable. These defects are
   fixed in release 2.4(3) and all subsequent releases. Free upgrades are
   offered to all affected customers as shown below. In lieu of an
   upgrade, several workarounds are available that might minimize the
   threat imposed by these defects.

   CiscoSecure ACS for UNIX is not affected by these vulnerabilities.

   This advisory is available at

Affected Products

   The defects described in this document are present in releases 2.1(x),
   2.3(3), and 2.4(2) of CiscoSecure ACS for Windows NT Server, as well
   as all earlier releases.

   The previously-mentioned releases of CiscoSecure ACS are vulnerable
   only if they are running on Windows NT Server. CiscoSecure ACS for
   UNIX is specifically not at risk due to these vulnerabilities.

   All three defects have been repaired in release 2.4(3). All subsequent
   releases of CiscoSecure ACS for Windows NT Server will include the


          A buffer overflow condition within the CSAdmin module can be
          exploited by sending an oversized packet to TCP port 2002 of
          CiscoSecure ACS Server for Windows NT. Depending on the exact
          version of the underlying NT operating system, it may be
          possible to force the execution of inserted code or to
          temporarily crash the module. Any existing administrative
          sessions will be terminated when a crash occurs, which may lead
          to the loss of recent administrative actions. In versions
          2.3(x) and higher, the CSAdmin module is restarted
          automatically within one minute. Existing sessions are
          re-established at that time, but the must be authenticated
          again as though they have started from the beginning. In
          earlier versions, the server must be restarted.
          This vulnerability can be triggered without any authentication
          at all, although authentication is normally required for all
          expected activities.

          By sending an oversized TACACS+ packet to CiscoSecure ACS for
          Windows NT Server it is possible to place the system into an
          unstable condition that may lead to a denial of service. In
          order to exploit this vulnerability, the attacker must be able
          to sniff or inject traffic into the path between the TACACS+
          client and CiscoSecure ACS for Windows NT Server.

          Some Lightweight Directory Access Protocol (LDAP) servers allow
          users to have a password that is undefined, meaning that the
          value of the stored password is null. An interaction between
          such an LDAP server and this defect may allow enable-mode
          authentication to succeed without specifying a valid password
          for that privileged mode.


   The following descriptions apply to all installations of CiscoSecure
   ACS for Windows NT Server. Installations of CiscoSecure ACS for UNIX
   are unaffected.

          This defect can be exercised repeatedly to create a denial of
          service attack, thus affecting the availability of the server.
          Depending on specific Windows NT installation details, this
          defect can allow the unauthorized execution of arbitrary
          commands. This can be exploited to gain access to or modify
          data without appropriate authorization, thus possibly violating
          the confidentiality or integrity of the server.

          This defect may be exercised repeatedly to create a denial of
          service attack, thus affecting the availability of the system.

          If an LDAP server that allows null passwords is in use as
          described previously, then this defect can be exploited to
          escalate privileges on a network device without authorization.

Software Versions and Fixes

   All versions of CiscoSecure ACS for Windows NT Server prior to release
   2.4(3) are affected by all three vulnerabilities. Customers that are
   using any version earlier than release 2.4(3) should upgrade to
   2.4.(3) or higher.

   Customers that are running any version of CiscoSecure ACS for UNIX are
   not vulnerable to the defects described in this security advisory.

Obtaining Fixed Software

   Cisco is offering free software upgrades to eliminate this
   vulnerability for all affected customers.

   Customers with contracts should obtain upgraded software through their
   regular update channels. For most customers, this means that upgrades
   should be obtained via the Software Center on Cisco's Worldwide Web
   site at http://www.cisco.com/.

   Customers without contracts should get their upgrades by contacting
   the Cisco Technical Assistance Center (TAC) 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 () cisco com

   http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml contains
   additional contact information for the TAC, including instructions and
   e-mail addresses for use by non-English speakers.

   Give the URL of this notice as evidence of your entitlement to a free
   upgrade. Free upgrades for non-contract customers must be requested
   through the TAC.

   Please do not contact either "psirt () cisco com" nor
   "security-alert () cisco com" for software upgrades. Faster results will
   be obtained by contacting the TAC.

   Customers planning to upgrade should refer to the release notes and
   other relevant documentation before beginning the upgrade to be
   certain that all hardware and software requirements for the newer
   version have been satisfied.


   The following workarounds will assist in mitigating threats due to
   these vulnerabilities, but cannot completely eliminate the potential
   for successful exploitation of the defects. Customers with affected
   systems are strongly recommended to upgrade to unaffected, fixed
   versions of the software as listed previously in this security
   advisory. In lieu of upgrading the software, the following steps may
   help minimize the risk:

          To protect the CSAdmin module from oversized URLs, limit access
          to the CiscoSecure ACS server so that only computers with
          legitimate need can reach it via the network. This can be
          accomplished by placing an Access Control List (ACL) on a
          router between the CiscoSecure ACS server and the remainder of
          the network. In the following example, the CiscoSecure ACS
          server has an IP address of and is attached to the
          Ethernet0 interface of an adjacent router. The terminal server
          has an address of Access between the terminal server
          and the CiscoSecure ACS server can be prevented by entering
          config mode from enable mode and using commands similar to the
          following partial list of instructions to create an ACL and
          apply it to the router's Ethernet0 interface:

              access-list 200 permit ip host host eq 49
              access-list 200 deny any any log

              interface Ethernet0
              ip access-group 200 incoming

          The CiscoSecure ACS server can be protected from receiving an
          oversized TACACS+ packet by applying an ACL on an adjacent
          router as shown above, or by implementing access controls on a
          firewall device that considers the ACS to be part of its
          protected network.

          An additional method is to ensure that a trusted path exists
          between the CiscoSecure ACS for Windows NT Server and the
          devices that are using it. This is a prudent measure to prevent
          sniffing or injection of packets along that path.

          Unauthorized enable access due to this defect can be thwarted
          by storing the enable password directly on the CiscoSecure ACS
          for Windows NT Server itself rather than on the remote LDAP

Exploitation and Public Announcements

   The Cisco PSIRT is not aware of any public announcements or malicious
   use of the vulnerabilities described in this advisory.

Status of This Notice: FINAL

   This is a final notice. Although Cisco cannot guarantee the accuracy
   of all statements in this notice, all of the facts have been checked
   to the best of our ability. Cisco does not anticipate issuing updated
   versions of this notice unless there is some material change in the
   facts. Should there be a significant change in the facts, Cisco may
   update this notice.


   This notice will be posted at
   http://www.cisco.com/warp/public/707/csecureacsnt-pub.shtml. In
   addition to Worldwide Web posting, a text version of this notice will
   be clear-signed with the Cisco PSIRT PGP key and posted to the
   following e-mail and Usenet news recipients:
     * cust-security-announce () cisco com
     * bugtraq () securityfocus com
     * firewalls () lists gnac com
     * first-teams () first org (includes CERT/CC)
     * cisco () spot colorado edu
     * cisco-nsp () puck nether net
     * comp.dcom.sys.cisco
     * Various internal Cisco mailing lists

   Future updates of this notice, if any, will be placed on Cisco's
   Worldwide Web server, but may or may not be actively announced on
   mailing lists or newsgroups. Users concerned about this problem are
   encouraged to check the URL given above for any updates.

Revision History

   Revision 1.0 2000-09-19 Candidate for initial public release
   Revision 1.1 2000-09-20 Minor corrections
   Revision 1.2 2000-09-21 Spelling and grammatical corrections, major
   changes to workarounds

Cisco Product Security Incident Assistance Process

   describes how to report security vulnerabilities in Cisco products,
   obtain assistance with security incidents, and register to receive
   product security information from Cisco Systems, Inc., including
   instructions for press inquiries regarding Cisco security advisories
   and notices. This advisory is Cisco's official public statement
   regarding this vulnerability.

   This notice is Copyright 2000 by Cisco Systems, Inc. This notice may
   be redistributed freely after the release date given at the top of the
   text, provided that redistributed copies are complete and unmodified
   and include all date and version information.

Version: PGP 6.5.2

Version: PGP 6.5.2


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