PowerDNS Security Advisory 2006-01: Malformed TCP queries can lead to a buffer overflow which might be exploitable

• CVE: CVE-2006-4251
• Date: 13th of November 2006
• Affects: PowerDNS Recursor versions 3.1.3 and earlier, on all operating systems.
• Not affected: No versions of the PowerDNS Authoritative Server (‘pdns_server’) are affected.
• Severity: Critical
• Impact: Potential remote system compromise.
• Exploit: As far as we know, no exploit is available as of 11th of November 2006.
• Solution: Upgrade to PowerDNS Recursor 3.1.4, or apply the patches referred below and recompile
• Workaround: Disable TCP access to the Recursor. This will have slight operational impact, but it is likely that this will not lead to meaningful degradation of service. Disabling access is best performed at packet level, either by configuring a firewall, or instructing the host operating system to drop TCP connections to port 53. Additionally, exposure can be limited by configuring the allow-from setting so only trusted users can query your nameserver.

PowerDNS Recursor 3.1.3 and previous miscalculate the length of incoming TCP DNS queries, and will attempt to read up to 4 gigabytes of query into a 65535 byte buffer.

We have not verified if this problem might actually lead to a system compromise, but are acting on the assumption that it might.

For distributors, a minimal patch is available on the PowerDNS wiki. Additionally, those shipping very old versions of the PowerDNS Recursor might benefit from this patch.

The impact of these and other security problems can be lessened by considering the advice in FIXME: security-settings.