Advisory ID: cisco-sa-20000921-secure-acs-nt
For Public Release 2000 September 21 17:00 UTC (GMT)
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
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
This section provides details on 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
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.
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
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.
Cisco has provided scores for the vulnerabilities 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
Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
The following descriptions apply to all installations of CiscoSecure
ACS for Windows NT Server. Installations of CiscoSecure ACS for UNIX are
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.
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.
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 184.108.40.206 and is attached to the Ethernet0 interface of an adjacent router.
The terminal server has an address of 220.127.116.11. 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 18.104.22.168 host 22.214.171.124 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 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
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.
Cisco has made free software available to address this vulnerability
for affected customers. 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
or as otherwise set forth at Cisco.com Downloads at
Do not contact either "email@example.com" or "firstname.lastname@example.org"
for software upgrades.
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
Customers whose Cisco products are provided or maintained through prior
or existing agreement 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 who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors but are
unsuccessful at obtaining fixed software through their point of sale should get
their 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)
Have your product serial number available and 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.
for additional TAC contact information, including special localized telephone
numbers and instructions and e-mail addresses for use in various
The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerabilities described in this advisory.
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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.
This advisory will be posted on Cisco's worldwide website at
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.
email@example.com (includes CERT/CC)
Various internal Cisco mailing lists
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
for any updates.
Edited to ask customers to contact the TAC to obtain fixed
Initial public release.