COMMAND
Cisco
SYSTEMS AFFECTED
CiscoSecure ACS for Windows NT Server
PROBLEM
Following is based on a Cisco Security Advisory. 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.
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.
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.
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.
This defect may be exercised repeatedly to create a denial of
service attack, thus affecting the availability of the system.
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.
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.
SOLUTION
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.
Customers that are using any version earlier than release 2.4(3)
should upgrade to 2.4.(3) or higher. Cisco is offering free
software upgrades to eliminate this vulnerability for all affected
customers.
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.