critical severityConfidence highHistorical record

Unbound DNSKEY digest overflow can RCE resolvers

NLnet Labs Unbound through 1.26.0 can overflow a digest buffer while validating a malicious DNSKEY (owner compression pointer into its own RDATA), enabling DoS and possible remote code execution when the resolver digests attacker-controlled zone data. Upgrade to Unbound 1.26.1 or later.

Also tracked as CVE-2026-81642 · Unbound DNSKEY RCE

First observed

Sep 16, 2026

Last observed

Sep 16, 2026

Last reviewed

Sep 20, 2026

Tracking ended

Sep 16, 2026

JSON recordArtifact CSVSTIX 2.1 bundle

Uncertainty and limitations

Read the evidence limits before acting on this record.

Remote code execution requires attacker-controlled zone data reaching the validator; packaging lag means distro packages may still ship 1.26.0 until rebuilds land.

  • Only validating Unbound instances that process attacker-influenced DNSKEYs are in scope.
  • OS package rebuilds may lag the upstream 1.26.1 tag.
  • This campaign does not cover unrelated Unbound CVEs in the same release train.

Timeline

Reviewed events, oldest first, each tied to a verified source.

  1. Disclosure

    NLnet Labs published CVE-2026-81642 for Unbound DNSKEY digest buffer overflow.

  2. Vendor action

    Fixed in Unbound 1.26.1 per vendor advisory.

  3. Update

    HOL Guard published operator blog and social coverage for CVE-2026-81642.

Publication clock: 100.3 hours from reviewed disclosure timestamp to HOL publication; 12-hour critical target; historical backfill outside target.

Guard coverage and non-coverage

What Guard's reviewed coverage assertions do and do not claim for this campaign.

No Guard coverage mapping is published for this record.

Defensive policy guidance

Reviewed starting points for defending against this campaign's artifact classes.

No campaign-specific policy guidance is published.

Reviewed artifacts and indicators

Published values are defanged (for example hxxps and [.] blocks) so nothing here is copy-paste executable.

Reviewed artifacts

The specific artifacts this record concerns, as reviewed. Names and versions are shown as text; a registry link is not recorded here.

  • unbound@<=1.26.0nativepackage

Sources

Every claim on this record is traceable to the sources below.

Reviewed in full by HOL Guard Security Publishing.

Published
Last full review
Last modified

Report a correction

Record HGTC-2026-8F7CDB8E.