The recent privacy stuff-up in Messenger "pales in comparison to what can be done if you use MSN Messenger through unpatched IE vulnerabilities," security researchers Tom Gilder and Thor Larholm have discovered.
Among the fun and games one can have with a vulnerable Messenger user are such sports as impersonating the victim and sending spoof messages and spoof e-mail memos to his contacts, and scouring his local drive for interesting files to share around.
In other words, you can do anything with the victim's Messenger client that the owner can do.
A demonstration has been set up here.
The problem is not a bug in Messenger, but one in IE, namely the Document.Open() vulnerability discovered in mid-December by ThePull, which allows for cookies to be gathered and documents to be read. This one is demonstrated here.
There is not yet a patch for this and several other IE holes. Vulnerable systems include:
Windows 98 SE with IE6 final (fully patched as of Feb 9) and MSN Messenger 4.6.0073
Windows 98 SE with IE6 final and MSN Messenger 3.6.0024
Windows ME with IE6 final (fully patched as of Feb 9) and MSN Messenger 4.5.0127
Windows 2000 with IE6 final (fully patched as of Feb 9) and MSN Messenger 4.6.0071
Windows 2000, IE5.5, MSN Messenger 4.6.00.73
Interestingly, MS released a major IE patch late last week but quickly removed it. Whether this was because they'd neglected to address this exploit or because the patch was ineffective or because it breaks people's computers we don't know.
A handy reference of yet-to-be-patched IE flaws can be reviewed here. IE users may wish to compare it against the next IE patch, when MS finally gets it sorted out.