CVE-2026-81634: Nlnetlabs Unbound

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

Affected products

• Nlnetlabs Unbound: before 1.26.1 (fixed in 1.26.1)

Published 2026-09-16. Last modified 2026-09-23.