Command injection through URL in Pidgin
tomkiewi at gmail.com
Sun Jun 9 13:41:18 EDT 2013
2013/6/9 John Houwer <john.houwer at gmail.com>:
> I'm using fluxbox.
> execve("/usr/bin/xdg-open", ["xdg-open", "http://127.0.0.1/`date`"], [/* 73
> vars */] <unfinished ...>
> If I run a URL from claws-mail I get:
> execve("/usr/bin/xdg-open", ["xdg-open", "http://127.0.0.0/$%28xterm%29"],
> [/* 74 vars */] <unfinished ...>
> xdg-open is a /bin/sh shell script, if it gets executed I'm pretty sure the
> arguments get interpreted before any code from the script is run.
> I can see that one can argue that xdg-open is broken, and maybe it is. I
> believe in multilayer security! In my opinion xdg-open should not have this
> design and pidgin should escape this stuff.
> As it is now, xdg-open relies on validated input. This is a bad decision,
> but so does the shell. ;)
I checked it on my system and xdg-open doesn't seems to be broken (but
I may be wrong). I've also checked original packages  and they
seems different from mine (openSUSE). So, I assume, every linux
distribution have its own - could you provide yours? Optimally, you
could provide all xdg-* scripts.
> I don't have a gnome or kde setup near me, so I don't know if the problem
> exists there too.
> Regards John
> On Sun, Jun 9, 2013 at 6:49 PM, Tomasz Wasilczyk <tomkiewi at gmail.com> wrote:
>> 2013/6/9 Ethan Blanton <elb at pidgin.im>:
>> > John Houwer spake unto us the following wisdom:
>> >> http://example.org/$(xterm)
>> >> opens a xterm (linux)
>> >> http://example.org/$(touch<tab>/tmp/ownage)
>> >> Creates the File /tmp/ownage! If you use a <space> the URL will stop.
>> >> If
>> >> you use a <tab> you can inject what you want to.
>> >> In preferences the browser is set to "desktop default".
>> >> I think this is a major concern. The user needs to click on the link,
>> >> but
>> >> you know how it is nowadays. ;)
>> > This is a major concern. We should be inoculated from this, but there
>> > may be a bug. It is also possible that there's a bug in the desktop
>> > handler, or in the program/script handling the ultimate URL. What
>> > desktop environment are you using? On gnome we use gnome-open, and on
>> > KDE we use kfmclient; in both cases, the URL is escaped with
>> > g_shell_quote. Can you get a strace of this process, with arguments,
>> > and find the exec we're actually invoking?
>> > In general, though, I don't like this code. We should ultimately be
>> > reducing to execv, not exec. It looks like we're using
>> > g_spawn_command_line_sync, and we should be using g_spawn_sync.
>> > Regardless of where the bug lies in this (in our code or in the
>> > desktop), this should be changed.
>> What do you think, if I would rewrite that code to use execv (of
>> course, hidden behind glib)?
>> > Ethan
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