Summary

• 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 CSCdr68286.
    
  • 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 https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20000921-secure-acs-nt.

Affected Products

• This section provides details on affected products.

  Vulnerable 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.

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

  Products Confirmed Not Vulnerable

  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.

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

Details

• CSCdr68286

  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.

  CSCdr51286

  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.

  CSCdr26113

  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.

Workarounds

• 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:

  CSCdr68286

  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 1.1.1.1 and is attached to the Ethernet0 interface of an adjacent router. The terminal server has an address of 2.2.2.2. 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 2.2.2.2 host 1.1.1.1 eq 49
      access-list 200 deny any any log
      
      interface Ethernet0
      ip access-group 200 incoming
  
  

  CSCdr51286

  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.

  CSCdr26113

  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 server.

Fixed Software

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

Exploitation and Public Announcements

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

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20000921-secure-acs-nt

Revision History

• Revision 1.3	2000-October-20	Edited to ask customers to contact the TAC to obtain fixed software.
  Revision 1.2	2000-September-21	Initial public release.

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