Quick answers
- Is CVE-2026-81634 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-81634 being exploited in the wild.
- How severe is CVE-2026-81634?
- High severity, with a CVSS score of 7.5, published 16 September 2026.
- Which products and versions are affected?
- NLnet Labs Unbound up to and including 1.26.0.
- Is there a fix for CVE-2026-81634?
- A patch was published on 2026-09-16: Unbound 1.26.1 released with fix Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-81634 attacked?
- It is attacked over the network or from the adjacent network.
- Am I affected by CVE-2026-81634?
- Check whether you run NLnet Labs Unbound at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
This is a heap buffer overflow vulnerability in the RRSet canonicalisation routine of Unbound. The root cause is a missing length check for the first owner name when validating buffer boundaries during canonicalisation. An attacker can craft a 255-byte query name with a large TCP response to overflow the heap buffer. The attack requires either a compromised upstream name server or the ability to intercept and modify DNS responses in transit (before DNSSEC validation occurs). An attacker can trigger a denial of service or potentially achieve code execution. The fix is available in Unbound 1.26.1, which adds the missing owner name to the buffer length check.
Affected products
- NLnet Labs Unbound up to and including 1.26.0
Timeline
- 2026-09-16: disclosed
- 2026-09-16: patched: Unbound 1.26.1 released with fix