PowerDNS Security Advisory 2016-02: Crafted queries can cause abnormal CPU usage

• CVE: CVE-2016-7068
• Date: December 15th 2016
• Credit: Florian Heinz and Martin Kluge
• Affects: PowerDNS Authoritative Server up to and including 3.4.10, 4.0.1, PowerDNS Recursor up to and including 3.7.3, 4.0.3
• Not affected: PowerDNS Authoritative Server 3.4.11, 4.0.2 and PowerDNS Recursor 3.7.4, 4.0.4
• Severity: Medium
• Impact: Degraded service or Denial of service
• Exploit: This issue can be triggered by sending specially crafted query packets
• Risk of system compromise: No
• Solution: Upgrade to a non-affected version
• Workaround: Run dnsdist with the rules provided below in front of potentially affected servers.

An issue has been found in PowerDNS allowing a remote, unauthenticated attacker to cause an abnormal CPU usage load on the PowerDNS server by sending crafted DNS queries, which might result in a partial denial of service if the system becomes overloaded. This issue is based on the fact that the PowerDNS server parses all records present in a query regardless of whether they are needed or even legitimate. A specially crafted query containing a large number of records can be used to take advantage of that behaviour. This issue has been assigned CVE-2016-7068.

PowerDNS Authoritative Server up to and including 3.4.10 and 4.0.1 are affected. PowerDNS Recursor up to and including 3.7.3 and 4.0.3 are affected.

dnsdist can be used to block crafted queries, using RecordsCountRule() and RecordsTypeCountRule() to block queries with crafted records.

For those unable to upgrade to a new version, a minimal patch is available

We would like to thank Florian Heinz and Martin Kluge for finding and subsequently reporting this issue.