Date: Wed, 12 Aug 2015 17:00:34 +0200 From: Robert Święcki <robert@...ecki.net> To: oss-security@...ts.openwall.com Cc: Andy Lutomirski <luto@...capital.net>, Daniel Kahn Gillmor <dkg@...thhorseman.net>, Kurt Seifried <kseifried@...hat.com> Subject: Re: Re: Terminal escape sequences - the new XSS for admins? 2015-08-11 23:59 GMT+02:00 Steve Grubb <sgrubb@...hat.com>: > On Tuesday, August 11, 2015 02:40:12 PM Andy Lutomirski wrote: > > > At this point, I was convinced that most major emulators are safe. That > > > said...there are all the ones I didn't check including older ones. The > > > older ones are likely to be the ones I'd be most concerned about. > > > > Are all the supposedly invulnerable terminals actually safe? > > Gnome-terminal reports: > > > > 0000000: 1b5d 6c54 6572 6d69 6e61 6c1b 5c .]lTerminal.\ > > > > That's not as bad as echoing 'ls -al' back to the terminal input, but > > why is it considered acceptable for terminals to input anything > > whatsoever in response to the in-band data they receive? > > The whole idea is to write something that you can bounce back to the > prompt. > lTerminal is pretty limiting. An attacker would have to also place the file > lTerminal in the search path before using this trick. But if they can do > pre- > place a file in the search path, they can also take advantage of typing > mistakes like placing a file vo and then waiting for the admin to make a > mistake typing vi. > > What you really want to do in an attack is to try placing a call back > shell > command on the prompt or download/upload files. > > Most terminal emulators, konsole for example, reply with nothing. Its the > vte > based ones that reply like this. I was reviewing the code and fuzzing various terminal emulators quite extensively some time ago, and found that "only" rxvt might be susceptible to this (if I remember correctly, there's typo in the code that enables this). $ echo -ne "\eGQ;" ;$ 0 bash: 0: command not found If you manage to append some arbitrary bytes to the input queue (except 0 and meaningless sequences like echo -ne "\e[6n\eGQ;"), then this sequence can be used to execute your command. As for other terminal emulators, I was able to crash most of them, and from what I see I still have testcases for konsole, pterm, rxvt, securecrt and xterm. I was looking for command injections though, so simply forgot to submit the testcases to the maintainers of the code after the exercise. I'll do that shortly. -- Robert Święcki
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