GNU bug report logs - #47584
Race condition in ‘copy-account-skeletons’: possible privilege escalation.

Previous Next

Full log

View this message in rfc822 format

From: Ludovic Courtès <ludo <at> gnu.org>
To: Maxime Devos <maximedevos <at> telenet.be>
Cc: 47584 <at> debbugs.gnu.org
Subject: bug#47584: Race condition in ‘copy-account-skeletons’: possible privilege escalation.
Date: Sat, 03 Apr 2021 22:33:18 +0200

Maxime Devos <maximedevos <at> telenet.be> skribis:

> The attack consists of the user being logged in after the account
> skeletons have been copied to the home directory, but before the
> owner of the account skeletons have been set.  The user then deletes
> a copied account skeleton (e.g. @file{$HOME/.gdbinit}) and replaces
> it with a symbolic link to a file not owned by the user, such as
> @file{/etc/shadow}.
>
> The activation code then changes the ownership
> of the file the symbolic link points to instead of the symbolic
> link itself.  At that point, the user has read-write access
> to the target file.

In the draft blog post, you mention that the attack cannot be carried
out when protected symlinks are enabled.  This is now the case by
default on Guix System¹, so in that case, a system upgraded from a
commit after March 16th is unaffected.

Ludo’.

¹ https://issues.guix.gnu.org/47013#13

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.