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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
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Cisco Security Advisory: Multiple Vulnerabilities in CiscoSecure ACS for
Windows NT Server
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
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
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
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
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 126.96.36.199 and is attached to the
Ethernet0 interface of an adjacent router. The terminal server
has an address of 188.8.131.52. 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 184.108.40.206 host 220.127.116.11 eq 49
access-list 200 deny any any log
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
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
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
* 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 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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- Cisco Security Advisory: Multiple Vulnerabilities in CiscoSecure ACS for Windows NT Server Cisco Systems Product Security Incident Response Team (Sep 22)