Date: Tue, 11 Aug 2015 14:40:12 -0700 From: Andy Lutomirski <luto@...capital.net> To: oss security list <oss-security@...ts.openwall.com> Cc: Daniel Kahn Gillmor <dkg@...thhorseman.net>, Kurt Seifried <kseifried@...hat.com> Subject: Re: Terminal escape sequences - the new XSS for admins? On 08/11/2015 01:29 PM, Steve Grubb wrote: > On Tuesday, August 11, 2015 04:13:48 PM Daniel Kahn Gillmor wrote: >> On Tue 2015-08-11 12:23:59 -0400, Kurt Seifried wrote: >>> So we've had a bunch of this stuff over the years: >>> >>> http://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=terminal+escape >>> >>> And now more recently: >>> >>> http://turbochaos.blogspot.ca/2014/08/journalctl-terminal-escape-injection >>> .html https://bugzilla.redhat.com/show_bug.cgi?id=1084577 >>> >>> And we have at least one more coming down the pipeline that's pretty >>> widespread. >>> >>> Also I'm thinking of all those docker apps that log to STDOUT. >>> >>> So the basic TL;DR: please don't use really ancient terminal programs that >>> are vulnerable to this stuff. It appears in testing that most (all?) of >>> the >>> Red Hat stuff is ok, but I can't speak for other vendors. >> >> Do we have a catalog of terminal programs that are vulnerable, or of >> particularly dangerous escape sequences to test with each terminal >> emulator? > > echo $'\e[30m' - turns foreground black (used to trick people by hiding > text) > echo $'\e]2;ls -al\a' - set window title to 'ls -al' > echo $'\e[21t' - print the window title to the command prompt. This is the one > to watch out for. > > In my survey recently, Some emulators could set the window title; none of them > supported reading the window title back to the command prompt. If you find one > that does, it is one that is at risk. > > Also note that an attempt to foil or make it hard to set window titles is in > bashrc under something called PROMPT_COMMAND. You may have to export > PROMPT_COMMAND="" and then start a new shell to launch the terminal windows. > > In my survey over the weekend, I used Fedora 22 and tested the following: > > xterm - not vulnerable > gnome-terminal - not vulnerable > konsole - not vulnerable > terminator - not vulnerable. > qterminal - not vulnerable (Undecodable sequence: \001b(hex)[21t) > Eterm - not vulnerable > rxvt - not vulnerable > st - not vulnerable (erresc: unknown csi ESC[21t) > lilyterm - not vulnerable > sakura - not vulnerable > caja-terminal - not vulnerable > xfce4-terminal - not vulnerable > roxterm - not vulnerable > mate-terminal - not vulnerable > termit - not vulnerable > > A lot were based on the vte package. So, I dug into the vte package. In the > file, vteseq.c, is this: > > case 21: > /* Report a static window title, since the real > window title should NEVER be reported, as it > creates a security vulnerability. See > http://marc.info/?l=bugtraq&m=104612710031920&w=2 > and CVE-2003-0070. */ > _vte_debug_print(VTE_DEBUG_PARSE, > "Reporting fake window title.\n"); > /* never use terminal->window_title here! */ > g_snprintf (buf, sizeof (buf), > _VTE_CAP_OSC "lTerminal" _VTE_CAP_ST); > vte_terminal_feed_child(terminal, buf, -1); > break; > > 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? --Andy
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