Rule:

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Sid:
2040

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Summary:
This event is generated when an attempt is made to login using XTACACS
from a machine outside the local area network.

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Impact:
This may be an intelligence gathering activity or an attempt to access 
resources controlled by the XTACACS server.

This may also be an attempt to gain unauthorized access to resources 
with the credentials of a valid user using brute force methodology.

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Detailed Information:
The Extended Terminal Access Controller Access Control System (XTACACS) 
is an authentication and authorization protocol derived from  CISCO 
TACACS. It is used in tcp/ip networks where network servers authenticate
clients from a master server.

When a user logs in to a server that uses XTACACS the server then makes 
a request to a master server to detrmine the validity of the request. 
The master server then verifies the login attempt and returns data 
concerning that user which may include information regarding resources 
the user is allowed access to in the form of an access list.

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Affected Systems:
All servers using XTACACS for authentication control.

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Attack Scenarios:
Regular user login method.

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Ease of Attack:
Simple

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False Positives:

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False Negatives:
None Known

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Corrective Action:
XTACACS servers should only authenticate to known hosts and firewall 
rules should prevent access to XTACACS enabled servers from outside the 
local area network.

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Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

CERT:
http://www.cert.org/advisories/CA-2003-01.html

Network Information Library - Intel:
http://www.intel.com/support/si/library/bi0414.htm

The Internet Next Generation Project:
http://ing.ctit.utwente.nl/WU5/D5.1/Technology/xtacacs/

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