PowerDNS Security Advisory 2017-01 for dnsdist: Crafted backend responses can cause a denial of serviceΒΆ

  • CVE: CVE-2016-7069
  • Date: 2017-08-21
  • Credit: Guido Vranken
  • Affects: dnsdist up to and including 1.2.0 on 32-bit systems
  • Not affected: dnsdist 1.2.0, dnsdist on 64-bit (all versions)
  • Severity: Low
  • Impact: Degraded service or Denial of service
  • Exploit: This issue can be triggered by sending specially crafted response packets from a backend
  • Risk of system compromise: No
  • Solution: Upgrade to a non-affected version
  • Workaround: Disable EDNS Client Subnet addition

An issue has been found in dnsdist in the way EDNS0 OPT records are handled when parsing responses from a backend. When dnsdist is configured to add EDNS Client Subnet to a query, the response may contain an EDNS0 OPT record that has to be removed before forwarding the response to the initial client. On a 32-bit system, the pointer arithmetic used when parsing the received response to remove that record might trigger an undefined behavior leading to a crash.

dnsdist up to and including 1.1.0 is affected on 32-bit systems. dnsdist 1.2.0 is not affected, dnsdist on 64-bit systems is not affected.

For those unable to upgrade to a new version, a minimal patch is available for 1.1.0

We would like to thank Guido Vranken for finding and subsequently reporting this issue.