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Home : Advisories : Multiple Vulnerabilities in CiscoSecure ACS for Windows NT Server

Title: Multiple Vulnerabilities in CiscoSecure ACS for Windows NT Server
Released by: Cisco
Date: 21st September 2000
Printable version: Click here

   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.html 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.html. 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.



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