Microsoft MSN Messenger is prone to a remote buffer-overflow vulnerability when handling malformed Graphic Interchange Format (GIF) images. This may allow an attacker to gain unauthorized access to an affected computer by executing arbitrary code, reportedly resulting in system-level compromise. Specially crafted emoticons or display pictures are likely to be used in a client-to-client attack. Other attack vectors may exist as well. MSN Messenger 6.2 and MSN Messenger 7.0 beta are vulnerable.
Block external access at the network boundary, unless external parties require service.
MSN Messenger communications may be blocked at the network perimeter. This may reduce exposure to clients within the network. MSN Messenger communicates over TCP port 1863 when a direct connection is established. Blocking outgoing connections over port 1863 can block MSN Messenger communications.
Run all software as a nonprivileged user with minimal access rights.
Running all client software as a user with minimal privileges may help mitigate the impact of a successful exploit attempt.
Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to monitor network traffic for signs of anomalous or suspicious activity. This includes but is not limited to requests that include NOP sleds and unexplained incoming and outgoing traffic. This may indicate exploit attempts or activity that results from a successful exploit.
Do not accept or execute files from untrusted or unknown sources.
Avoid opening image files that originate from users of questionable integrity.
Do not accept communications that originate from unknown or untrusted sources.
Review MSN Messenger contact lists and remove unknown or undesired contacts.
Implement multiple redundant layers of security.
Various memory-protection schemes (such as nonexecutable and randomly mapped memory segments) may hinder an attacker's ability to exploit this vulnerability to execute arbitrary code.
Microsoft has released updates to address this vulnerability on supported platforms. UPDATE (January 22, 2009): Microsoft has updated its security bulletin to advise users that an update for MSN Messenger 6.2 is available via the download links in MS07-054 or by logging into the MSN Messenger service to accept the update.