oss-security - Re: Re: CVE assignment notification -- CVE-2010-0426 -- sudo improper pseudocommands file path check

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Date: Thu, 25 Feb 2010 15:49:25 -0600
From: Jamie Strandboge <jamie@...onical.com>
To: oss-security <oss-security@...ts.openwall.com>
Cc: "Todd C. Miller" <Todd.Miller@...rtesan.com>, "Steven M. Christey" <coley@...us.mitre.org>, Jan Lieskovsky <jlieskov@...hat.com>
Subject: Re: Re: CVE assignment notification --
 CVE-2010-0426 -- sudo improper pseudocommands file path check

On Tue, 2010-02-23 at 08:00 -0500, Todd C. Miller wrote:
> Here's my WIP writeup of this:
> 
> Summary:
> A flaw in exists in sudo's -e option (aka sudoedit) in sudo versions
> 1.6.9 through 1.7.2p3 that may give a user with permission to run
> sudoedit the ability to run arbitrary commands.
> 
> Sudo versions affected:
> 1.6.9 through 1.7.2p3 inclusive.

We have sudo 1.6.8p12 in a supported release of Ubuntu, and I noticed
that while 1.6.8p12 looked like it should be affected, I couldn't get
the reproducer[1] to work. I dug into it and found this:

In 1.6.9 we have in main() of sudo.c:
  execve(safe_cmnd, NewArgv, environ);

In 1.6.8p12 we have in main() of sudo.c:
  EXECV(safe_cmnd, NewArgv);  /* run the command */

In 1.6.8p12 EXECV can be either execv() or execvp() (there is a
configure option to choose which to use, it happened to default to
execvp() here). If you change the EXECV to be execv(), then the
reproducer works fine.  If you change the EXECV to be execvp(), then the
reproducer doesn't work.

From the eglibc manpage for execvp():
 The functions execlp() and execvp() will duplicate the actions of the
 shell in searching for an executable file if the specified filename
 does not contain a slash (/) character. The search path is the path
 specified in the environment by the PATH variable.

Looking at safe_cmnd in gdb (sudo_user.cmnd_safe) I found that it is
passing 'sudoedit' (ie, no '/' in the name) as the first argument, and
so execvp() is searching PATH for 'sudoedit' and exec'ing what it finds
rather than NewArgv[0] (in this case, './sudoedit').

In 1.6.8p12 PATH can be forced via the --secure-path configure option
for sudo, so if sudo is compiled with a sane --secure-path and
--with-execv=execvp, then it seems sudo is ok (though rather than
failing, it will edit the file as if './sudoedit' wasn't specified).
Without --secure-path, if sudo doesn't scrub PATH variable (eg using
env_keep=PATH) then it is vulnerable.

I did not check any other releases of 1.6.8 other than p12.

[1] http://sudo.ws/bugs/show_bug.cgi?id=389

-- 
Jamie Strandboge             | http://www.canonical.com

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