Windows Media Player Vulnerability

Another vulnerability has been posted for Windows Media Player, versions 9 and 10, and was originally only identified as a denial of service issue, Microsoft is evaluating whether it should rush out a fix for this flaw or not. Nothing has been posted about it for this Tuesday’s patch update.

Windows Media Player versions 9 and 10 are affected by the flaw, which could allow a malicious hacker to run unauthorized software on a victim’s PC or cause a denial of service attack, according to security company FrSIRT, which rated the problem critical in an advisory Thursday.

The flaw is due to a buffer overflow error that can occur when Windows Media Player is used to run “.asx” media files, according to a warning from eEye Digital Security. Source: Yahoo

The French Security Incident Response Team posted about this on Thursday here, Microsoft Windows Media Player ASX Playlist Remote Command Execution Vulnerability, the site is in French, so unless you can read it, I guess its a waste of time to visit. It was initially disclosed on 11/22/2006, according to eEye Digital Security, and had this to say about it.

The Windows Media Player library WMVCORE.DLL contains a potentially exploitable heap buffer overflow in its handling of “REF HREF” URLs within ASX files. If the URL contains an unrecognized protocol (only “file”, “ftp”, “http”, “https”, “mms”, “mmst”, “mmsu”, “rtsp”, “rtspt”, and “rtspu” appear to be recognized), the function at 7D7A8F27 in WMVCORE.DLL version, and at 086E586E in WMVCORE.DLL version, will create a copy of the string in which the protocol is replaced with “mms”. A heap buffer is allocated, the string “mms” is copied into it, and then everything after and including “://” in the “REF HREF” URL is concatenated using wcsncat.

Unfortunately, the heap buffer for the new “mms” URL is allocated to the size of the “REF HREF” URL, and even more unfortunately, the length of the input string being passed to wcsncat is supplied as the character count, effectively causing wcsncat to behave identically to wcscat. As a result, a two- or four-byte heap overflow is possible if the “REF HREF” URL features a protocol shorter than three characters (the length of “mms”).

Single-letter protocols (such as “a://”) are rejected, but this restriction can be circumvented by encoding the protocol (“%61://”), thereby making a four-byte overflow possible.

Exploitability due to the corruption of the adjacent heap block’s header is assumed likely but research is ongoing.

Users can upgrade to the latest version of Windows Media Player, here, version 11, which is not affected, or they can disable the automatic opening of “.asx” media files.