PowerDNS Security Advisory 2014-02: PowerDNS Recursor 3.6.1 and earlier can be made to provide bad service
- CVE: CVE-2014-8601
- Date: 8th of December 2014
- Credit: Florian Maury (ANSSI)
- Affects: PowerDNS Recursor versions 3.6.1 and earlier
- Not affected: PowerDNS Recursor 3.6.2; no versions of PowerDNS Authoritative Server
- 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 PowerDNS Recursor 3.6.2
- Workaround: None known. Exposure can be limited by configuring the allow-from setting so only trusted users can query your nameserver.
Recently we released PowerDNS Recursor 3.6.2 with a new feature that strictly limits the amount of work we'll perform to resolve a single query. This feature was inspired by performance degradations noted when resolving domains hosted by 'ezdns.it', which can require thousands of queries to resolve.
During the 3.6.2 release process, we were contacted by a government security agency with news that they had found that all major caching nameservers, including PowerDNS, could be negatively impacted by specially configured, hard to resolve domain names. With their permission, we continued the 3.6.2 release process with the fix for the issue already in there.
We recommend that all users upgrade to 3.6.2 if at all possible. Alternatively, if you want to apply a minimal fix to your own tree, it can be found here, including patches for older versions.
As for workarounds, only clients in allow-from are able to trigger the degraded service, so this should be limited to your userbase.