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Re: CVE request (and disclosure): ax25d missing setuid return code check
From: Ralf Baechle <ralf () linux-mips org>
Date: Thu, 11 Aug 2011 15:05:33 +0100

On Thu, Aug 11, 2011 at 02:13:23PM +0200, Thomas Osterried wrote:

Am Donnerstag, den 11. August 2011 um 07:20:41 Uhr, schrieb Eren Türkay <eren () pardus org tr> in 
<20110811052041.GB2043 () mutt-is@awesome>:
On Tue, Aug 09, 2011 at 11:33:04PM -0400, Dan Rosenberg wrote:
The AX.25 daemon (ax25d), typically provided in the ax25-tools
package, allows administrators to associate incoming AX.25, NET/ROM,
and ROSE traffic with the execution of an endpoint program (most
commonly "node"), which is run under a specified user account.
Because ax25d is missing a check on the return code for a setuid call
responsible for dropping privileges to the specified user, it may be
possible to cause setuid to fail, after which the chosen program will
be executed with root privileges.  In other words, if you're in the
business of handing out unprivileged shells over amateur radio (don't
we all? :p ), this would allow for remote compromise.

Hello,

Thank you for your investigation on the topic. Although this issue seems
to be low-priority, it's good to let the maintainers know.

I'm CCing Ralf Baechle, and Thomas Osterried who, accordingly to
linux-ac25 site, are the maintainers of ax25 utilities.

thank you for your information.

I know that code fragment, but I never imagined that if root calls
setuid/setgid that this could fail, because root has by definition enough
rights.

Welcome to the new world where things are more complicated ...

These days setuid and similar syscalls need to allocate memory for the
credentials of a process and memory allocations may fail.  A system could
even be put under massive memory pressure with the intend to make this
allocation fail.

Also setuid requires the capability CAP_SETUID which a process - running
as root or not may not have.

Finally a the Linux security subsystem has its say and while it's odd to
configure an LSM to reject the attempt to drop privileges it's entirely
possible.

  Ralf


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