Rule: -- Sid: 540 -- Summary: This event is generated when activity relating to network chat clients is detected. -- Impact: Policy Violation. Use of chat clients to communicate with unkown external sources may be against the policy of many organizations. -- Detailed Information: Instant Messaging (IM) and other chat related client software can allow users to transfer files directly between hosts. This can allow malicious users to circumvent the protection offered by a network firewall. Vulnerabilities in these clients may also allow remote attackers to gain unauthorized access to a host. -- Attack Scenarios: A user may transfer sensitive company information to an external party using the file transfer capabilities of an IM client. An attacker might utilize a vulnerability in an IM client to gain access to a host, then upload a Trojan Horse program to gain control of that host. -- Ease of Attack: Simple. -- False Positives: None Known -- False Negatives: None Known -- Corrective Action: Disallow the use of IM clients on the protected network and enforce or implement an organization wide policy on the use of IM clients. -- Contributors: Sourcefire Research Team Brian Caswell <brian.caswell@sourcefire.com> Nigel Houghton <nigel.houghton@sourcefire.com> -- Additional References: MSN Protocol http://www.hypothetic.org/docs/msn/ Devarticles http://www.devarticles.com/index2.php?option=content&task=view&id=225&pop=1&hide_ads=1&page=1 MSN Messenger Protocol http://www.venkydude.com/articles/msn.htm --