"That which is overdesigned, too highly specific, anticipates outcome; the anticipation of outcome guarantees, if not failure, the absence of grace."
-- William Gibson, All Tomorrow's Parties
Best disclosure ever.

[Full-disclosure] Local user to root escalation in apache 1.3.34 (Debian only)

Version 1.3.34-4 of Apache in the Debian Linux distribution contains a hole that allows a local user to access a root shell if the webserver has been restarted manually. This bug does not exist in the upstream apache distribution, and was patched in specifically by the Debian distribution. The bug report is located at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=357561 . At the time of writing (over a month since the root hole was clarified), there has been no official acknowledgement. It is believed that most of the developers are tied up in more urgent work, getting the TI-86 distribution of Debian building in
time for release.

Unlike every other daemon, apache does not abdicate its controlling tty on startup, and allows it to be inherited by a cgi script (for example, a local user's CGI executed using suexec). When apache is manually restarted, the inherited ctty is the stdin of the (presumably root) shell that invoked the new instance of apache. Any process is permitted to invoke the TIOCSTI ioctl on the fd corresponding to its ctty, which allows it to inject characters that appear to come from the terminal master. Thus, a user created CGI script can inject and have executed any input into the shell that spawned apache.

As a Debian user, this concerns me greatly, as any non-privileged user would be able to install non-free documentation (GFDL) on any system I run.


February 26, 2007 2:03 PM