msnmsgr.exe in Windows Live Messenger (WLM) 2009 build 14.0.8064.206, and other 14.0.8064.x builds, allows remote attackers to cause a denial of service (application crash) via a modified header in a packet, as possibly demonstrated by a UTF-8.0 value of the charset field in the Content-Type header line.  NOTE: this has been reported as a format string vulnerability by some sources, but the provenance of that information is unknown.