First and foremost: this requires the victim to click not one, but two random links sent to them over Pidgin (or any other program that does URL auto-linking the way Pidgin does). So it's not exactly the most severe vulnerability, but I found it interesting nonetheless.
.desktop files as their application launchers. They're plain text, INI-style files that describe the application's name, icon, and executable command.
A vulnerability was discovered a while back about Application Launchers, wherein a launcher file could be double-clicked on and it would run the command inside, in exactly the same way that a
.exe file can be double-clicked on Windows. And, like its Windows counterpart, it was easy to accidentally double-click an application launcher that you didn't intend to.
In the linked article's example, you could attach a
.desktop launcher to an e-mail in much the same way as a virus would, and a careless Linux user could accidentally run it just as easily.
In response, all of the Linux desktop environments made a change, so that you must explicitly mark an application launcher as "executable" before it can be double-clicked to run. Trying to run a non-executable launcher would result in a warning pop-up, telling you that the launcher is not trusted and giving you options to mark it executable, launch it anyway, or cancel.
Pidgin will take any text that looks like a URL, in the format
protocol://urlpath and make it into a clickable link. This includes
file://, but thankfully does NOT include
On Linux desktops, the underlying mechanism Pidgin uses is
xdg-open, which is the Linux version of the
open command on Mac OS X, or rough equivalent of the
start command on Windows. It will open anything using your preferred application, for example HTTP URLs will open in your default browser, text files in your default text editor, etc.
Also, Adium does the same thing for the Mac OS X users; have fun poking at that.
file:// URIs clickable;
xdg-open is the next part.
These were some of the behaviors I've seen with
xdg-open and what kinds of
file:/// links work in Pidgin:
file:///usr/bin/gedit) would execute the program on click.
file:///usr/bin/firefox -- a shell script), would NOT execute when clicked. Nothing would happen.
xdg-open will execute an application launcher (
.desktop) even when it isn't marked as executable.
.desktop file, by using the
Content-Disposition: attachment response header (this would likely need to be done via a PHP or CGI script).
~/Downloads in their home folder.
#!/usr/bin/env python print """Content-Type: application/octet-stream Content-Disposition: attachment; filename=Pwned.desktop [Desktop Entry] Type=Application Name=Pwned Exec=/usr/bin/bash -c 'echo "I pwned you :)" | /usr/bin/gedit -' """
For the xdg-open bug I filed a Red Hat bug ticket here. I'm half expecting to get a response back such as, "xdg-open simply forwards the request to your desktop environment's native file opener," but it is what it is.
file:// URI in them. When I was initially testing this, I was sending IMs to myself and noticed that any time I used a file URI, I didn't get my own message echoed back to me. For the proof of concept video, I used my personal XMPP server.
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