[Pdns-users] PowerDNS Security Advisory 2015-01
Peter van Dijk
peter.van.dijk at powerdns.com
Thu Apr 23 11:05:07 UTC 2015
Please be aware of PowerDNS Security Advisory 2015-01
(http://doc.powerdns.com/md/security/powerdns-advisory-2015-01/), which you
can also find below. The good news is that as far as we have seen, only
specific builds for RHEL5 are affected, but just to be sure we are doing
full releases of all recent versions of our products.
Packages and distribution tar balls of Recursor 3.6.3, Recursor 3.7.2 and Auth
3.4.4 are available in the usual places, and release announcements will be sent
out right after this email.
If you prefer a minimal patch, please go to
https://downloads.powerdns.com/patches/2015-01/ and see README.txt there.
If you have problems upgrading, please either contact us on our mailing lists,
or privately via powerdns.support at powerdns.com (should you wish to make use of
our SLA-backed support program).
We want to thank Aki Tuomi for finding this issue, and really digging into it.
We also want to thank Kees Monshouwer for assisting in debugging and fixing
the offending code. Finally we want to thank Kai Storbeck for putting an
earlier, broken version of the patch into production and being understanding
about the names that broke because of it.
PowerDNS Security Advisory 2015-01: Label decompression bug can cause crashes
on specific platforms
* CVE: CVE-2015-1868
* Date: 23rd of April 2015
* Credit: Aki Tuomi
* Affects: PowerDNS Recursor versions 3.5 and up; Authoritative
Server 3.2 and up
* Not affected: Recursor 3.6.3; Recursor 3.7.2; Auth 3.4.4
* Severity: High
* Impact: Degraded service
* Exploit: This problem can be triggered by sending queries for
specifically configured domains
* Risk of system compromise: No
* Solution: Upgrade to any of the non-affected versions
* Workaround: Run your Recursor under a supervisor. Exposure can be
limited by configuring the allow-from setting so only trusted
users can query your nameserver.
A bug was discovered in our label decompression code, making it
possible for names to refer to themselves, thus causing a loop during
decompression. This loop is capped at a 1000 iterations by a failsafe,
making the issue harmless on most platforms.
However, on specific platforms (so far, we are only aware of this
happening on RHEL5/CentOS5), the recursion involved in these 1000 steps
causes memory corruption leading to a quick crash, presumably because
the default stack is too small.
We recommend that all users upgrade to a corrected version if at all
possible. Alternatively, if you want to apply a minimal fix to your own
tree, please find patches here: https://downloads.powerdns.com/patches/2015-01/
These should be trivial to backport to older versions by hand.
As for workarounds, only clients in allow-from are able to trigger the
degraded service, so this should be limited to your userbase; further,
we recommend running your critical services under supervision such as
systemd, supervisord, daemontools, etc.
We want to thank Aki Tuomi for noticing this in production, and then
digging until he got to the absolute bottom of what at the time
appeared to be a random and spurious failure.
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