[rsbac] Fwd: [OT] rsync 2.5.6 security advisory

Amon Ott ao at rsbac.org
Thu Dec 4 10:29:22 CET 2003


Another example. The attacked rsync server was probably the exploited gentoo 
rsync server.


----------  Forwarded Message  ----------

Subject: [OT] rsync 2.5.6 security advisory
Date: Donnerstag, 4. Dezember 2003 10:02
From: Fabian Uebersax <fabian.uebersax at tiscali.ch>
To: linux-kernel at vger.kernel.org

From http://rsync.samba.org/ :

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 = 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 

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 

We recommend that anyone running a rsync server take the following steps:

   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 = no" then remove that line or change it to "use chroot = 
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 response:

    * Timo Sirainen <tss.iki.fi>
    * Mike Warfield <mhw.wittsend.com>
    * Paul Russell <rusty.samba.org>
    * Andrea Barisani <lcars.gentoo.org> 

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