Older versions of Yahoo! Messenger are subject to a security flaw that could allow crackers to run hostile code on vulnerable systems, according to security researchers.

The vulnerability stems from a buffer overflow bug in versions of Yahoo! Messenger earlier than 5.6.0.1351. The latest version (5.6.0.1358) of Yahoo! Messenger is immune to the problem but users of earlier versions reportedly cannot upgrade to the new version unless they reinstall the product.

Security researcher Tri Huynh of SentryUnion discovered the vulnerability. His advisory explains that flaw stems from a failure of earlier versions of Yahoo! Messenger in downloading files with excessively long file names.

This poor coding creates a means for malicious coders to crash machines running the application or run arbitrary code of vulnerable boxen, as explained here. ®