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Date: Thu, 10 Jul 2014 16:42:39 -0700
From: Tavis Ormandy <taviso@...xchg8b.com>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2014-0475: glibc directory traversal in LC_* locale handling

Rich Felker <dalias@...c.org> wrote:

> On Thu, Jul 10, 2014 at 08:52:24PM +0200, Florian Weimer wrote:
> > Stephane Chazelas discovered that directory traversal issue in locale
> > handling in glibc.  glibc accepts relative paths with ".." components in
> > the LC_* and LANG variables.  Together with typical OpenSSH
> > configurations (with suitable AcceptEnv settings in sshd_config), this
> > could conceivably be used to bypass ForceCommand restrictions (or
> > restricted shells), assuming the attacker has sufficient level of access
> > to a file system location on the host to create crafted locale
> > definitions there.
> 
> Am I correct in assuming this affects most typical git setups (e.g.
> gitolite) using ssh authorized_keys files with forced commands, where the
> malicious file could simply be created as part of the git repository? Or
> are these usually setup to filter the environment?
> 

I knew about this behaviour (I imagine lots of people were), but hadn't
considered it a vulnerability - it's more restricted across setuid, so had
assumed it was intentionally permitted. Locale files are not executable
code, so even if you imagine a ForceCommand+AcceptEnv configuration *and*
have the ability to create a message catalog, don't you still need another
bug to exploit this?

However, admittedly there was that zonefile parsing vulnerability and IIRC
TZ also permits directory traversal when not setuid. TZ is just as plausibly
part of AcceptEnv as LC_ALL, so maybe if it wasn't intentional there's at
least a weak argument there for calling it a glibc vulnerability.

Anyway, if we're clearing up old unexploitable glibc bugs, here's another
one to consider. LD_PROFILE uses the inherited umask, so you can create
root-owned world writable files like this:

$ umask 0
$ LD_PROFILE=libc.so.6 su --version
su from util-linux 2.24.2
$ ls -l /var/profile
-rw-rw-rw-. 1 root taviso 18M Jul 10 16:12 libc.so.6.profile

I hadn't reported it as you have to have created /var/profile, and...

$ sudo yum whatprovides /var/profile
No matches found

But maybe some other distros have a package (or a bug that lets you create
directories), I havn't checked. There are a bunch of ways to abuse this if
you have /var/profile.

Tavis.

p.s. I think LD_HWCAP_MASK is still not in unsecure_vars :-)

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