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rsync 2.5.6 security advisory

December 4th 2003


The rsync team has received evidence that a vulnerability in rsync was
recently used in combination with a Linux kernel vulnerability to
compromise the security of a public rsync server. While the forensic
evidence we have is incomplete, we have pieced together the most
likely way that this attack was conducted and we are releasing this
advisory as a result of our investigations to date.

Our conclusions are that:

- rsync version 2.5.6 contains a heap overflow vulnerability that can
be used to remotely run arbitrary code.

- While this heap overflow vulnerability could not be used by itself
to obtain root access on a rsync server, it could be used in
combination with the recently announced brk vulnerability in the
Linux kernel to produce a full remote compromise.

- The server that was compromised was using a non-default rsyncd.conf
option "use chroot =3D no". The use of this option made the attack on
the compromised server considerably easier. A successful attack is
almost certainly still possible without this option, but it would
be much more difficult.

Please note that this vulnerability only affects the use of rsync as a
"rsync server". To see if you are running a rsync server you should
use the netstat command to see if you are listening on TCP port
873. If you are not listening on TCP port 873 then you are not running
a rsync server.

New rsync release

In response we have released a new version of rsync, version
2.5.7. This is based on the current stable 2.5.6 release with only the
changes necessary to prevent this heap overflow vulnerability. There
are no new features in this release.

We recommend that anyone running a rsync server take the following

1) update to rsync version 2.5.7 immediately

2) if you are running a Linux kernel prior to version 2.4.23 then
you should upgrade your kernel immediately. Note that some
distribution vendors may have patched versions of the 2.4.x
series kernel that fix the brk vulnerability in versions before
2.4.23. Check with your vendor security site to ensure that you
are not vulnerable to the brk problem.

3) review your /etc/rsyncd.conf configuration file. If you are
using the option "use chroot =3D no" then remove that line or
change it to "use chroot =3D yes". If you find that you need that
option for your rsync service then you should disable your rsync
service until you have discussed a workaround with the rsync
maintainers on the rsync mailing list. The disabling of the
chroot option should not be needed for any normal rsync server.

The patches and full source for rsync version 2.5.7 are available from
http://rsync.samba.org/ and mirror sites. We expect that vendors will
produce updated packages for their distributions shortly.


The rsync team would like to thank the following individuals for their
assistance in investigating this vulnerability and producing this

* Timo Sirainen

* Mike Warfield

* Paul Russell

* Andrea Barisani

The rsync team

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