Date: Tue, 27 Apr 1999 13:29:26 -0700 From: "LaFournaise, Chris J." To: BUGTRAQ@netspace.org Subject: NT/Exceed D.O.S. This is regarding Hummingbird's Exceed X emulator v5 (and possibly v6) running on Windows NT. I haven't tested Win95/98. The Exceed X server allows inbound TCP connections on port 6000 from the XDM host. If someone uses telnet from the XDM host to connect to a PC running Exceed on port 6000 and enters any garbage text, the X server will hang and the Exceed session is frozen for good. I have notified Hummingbird via their tech support web site but have not received a response yet. Chris LaFournaise cjlafournaise@escocorp.com ---------------------------------------------------------------------------- Date: Wed, 28 Apr 1999 23:34:26 +0100 From: Steve To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. > This is regarding Hummingbird's Exceed X emulator v5 (and possibly v6) > running on Windows NT. I haven't tested Win95/98. > > The Exceed X server allows inbound TCP connections on port 6000 from the XDM > host. If someone uses telnet from the XDM host to connect to a PC running > Exceed on port 6000 and enters any garbage text, the X server will hang and > the Exceed session is frozen for good. As far as I know, a variation of that bug has been present in all versions >from the early Exceed for MS-Dos onwards. I stumbled on it 5 years ago when I was a student, so I didn't know whether it was a configuration error or a bug. I don't think I managed to permanently freeze the connection then, but it was certainly possible to freeze it for as long as you left the telnet connection to port 6000 open. If I remember correctly, it didn't use to be just the XDM host that could make the connection, you could freeze Exceed >from any host. I guess that would depend on the setting of the 'Host Access Control List' field. For the record, I've just tested Exceed v6 under Windows 98 and it still has the same effect. I also tested setting Exceed to only allow a given machine to connect, and I can still freeze it by telnetting from another machine in another subnet... I didn't manage to freeze it beyond the telnet session to port 6000 though. Steve. ---------------------------------------------------------------------------- Date: Thu, 29 Apr 1999 09:23:11 -0600 From: Max Norris To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. I wasn't able to duplicate a mini-DOS running eXceed 6.0.2.0 on NT 4.0 SP4. Steps: On NT machine, opened xterm session Went to box that I just opened the session with, type in TELNET 6000 The eXceed program hung for about 2 minutes as the host tried to connect to it, but everything else still worked in NT. After attempting to connect, it will say it is connected for about 2 seconds and then states "Connection closed by foreign host". After that the eXceed session resumed and I was able to close out gracefully. Max Norris pedhrm.mnorris@state.ut.us >>> "LaFournaise, Chris J." 04/27 2:29 PM >>> This is regarding Hummingbird's Exceed X emulator v5 (and possibly v6) running on Windows NT. I haven't tested Win95/98. The Exceed X server allows inbound TCP connections on port 6000 from the XDM host. If someone uses telnet from the XDM host to connect to a PC running Exceed on port 6000 and enters any garbage text, the X server will hang and the Exceed session is frozen for good. I have notified Hummingbird via their tech support web site but have not received a response yet. Chris LaFournaise cjlafournaise@escocorp.com ---------------------------------------------------------------------------- Date: Wed, 28 Apr 1999 17:39:00 -0700 From: Ian Westcott To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. On Tue, Apr 27, 1999 at 01:29:26PM -0700, LaFournaise, Chris J. wrote: > This is regarding Hummingbird's Exceed X emulator v5 (and possibly v6) > running on Windows NT. I haven't tested Win95/98. > > The Exceed X server allows inbound TCP connections on port 6000 from the XDM > host. If someone uses telnet from the XDM host to connect to a PC running > Exceed on port 6000 and enters any garbage text, the X server will hang and > the Exceed session is frozen for good. I just tested Exceed v6.0 under Win95, and it is vulnerable. -- Ian Westcott | Fly away to a Rainbow in the sky. ijwestcott@ucdavis.edu | Gold is at the end for each of us to find. -==(UDIC)==- | There the road begins where another one will end. Rakarra@FurryMUCK, IRC | Here the four winds know, Dragon Code: DC.D f+ | Who will break and who will bend. s- h- Cgold>Red a $ | All to be the Master of the Wind. ---------------------------------------------------------------------------- Date: Wed, 28 Apr 1999 13:57:51 -0700 From: Matt Wilbur To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. Exceed (an X server, not an X emulator) version 6.0.1.0 on NT appears to have fixed this problem, somewhat... Telnetting to port 6000 locks the server up for 20-30 seconds, but it recovers eventually. Not surprisingly, using netcat has the same effect... although, contrary to Chris's findings with Exceed 5, I didn't need to send any garbage characters, the connection alone did the job. Also, it works >from any host, not just the one the xdm session had been initiated with, regardless of host access settings in Xconfig, Exceeds "configuration" tool. I'd still consider this DoS-bait, when you imagine a one-liner to continuously connect to port 6000 of your favorite Exceed user's machine. Matt Wilbur [snip] > > This is regarding Hummingbird's Exceed X emulator v5 (and possibly v6) > running on Windows NT. I haven't tested Win95/98. > > The Exceed X server allows inbound TCP connections on port > 6000 from the XDM> host. If someone uses telnet from the XDM host to connect to > a PC running Exceed on port 6000 and enters any garbage text, the X server > will hang and the Exceed session is frozen for good. > > I have notified Hummingbird via their tech support web site > but have not received a response yet. > > Chris LaFournaise > cjlafournaise@escocorp.com > ---------------------------------------------------------------------------- Date: Thu, 29 Apr 1999 11:54:14 -0700 From: Jamie Lawrence To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. I couldn't reproduce either effect with Exceed 6.1 under NTsp3. Everything behaved normally, both for new and existing sessions. -j ---------------------------------------------------------------------------- Date: Fri, 30 Apr 1999 16:20:21 -0400 From: Andrew Pitman To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. Jamie, Ditto for 6.1 on Win95. Appears to be fixed in 6.1, among other bugs, including an incompatibility with DEC Windows that was causing problems at my shop. Andrew -- "The wonderful thing about standards is that there are so many to choose from." (Andrew S. Tanenbaum) +-----------------------------+---------------------------------+ | Andrew Pitman | Management Information Systems, | | Unix System Administrator/ | Technology Operations Support | | Webmaster | at Rowan University | +-----------------------------+---------------------------------+ ---------------------------------------------------------------------------- Date: Sat, 1 May 1999 19:26:34 -0500 From: David Poythress To: BUGTRAQ@netspace.org Subject: Re: NT/Exceed D.O.S. This seems to have been fixed at some point, connecting and/or spewing random data to exceedhost 6000-6010 has no discenrible effect on exceed 6.1.0 under win98 or NTsp4. A denial of service is still possible though: Exceed defaults to allowing 128 connections from the xdm host, but counts a telnet connection as though it were a connection from a valid X client. Once the max number of connections is reached, subsequent attempts to the X port range are refused. -- David Poythress dp@qni.com "Grammar, which controls even kings ..." --Moliere