CVE-2026-77955
4.4 · MEDIUMIn NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack windo…
Overview
CVE-2026-77955 is a medium-severity vulnerability affecting nlnetlabs unbound. It was published on September 16, 2026 and has a CVSS 3.1 base score of 4.4 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 4.4, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
Technical description
In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads.
Remediation
Check the references section for vendor advisories and patches from nlnetlabs. Update unbound to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| nlnetlabs | unbound | >= 1.13.2, < 1.26.1 | Affected |
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Frequently asked questions
What is CVE-2026-77955?
CVE-2026-77955 is a medium-severity vulnerability affecting nlnetlabs unbound. It was published on September 16, 2026 and has a CVSS 3.1 base score of 4.4 (MEDIUM).
How severe is CVE-2026-77955?
This vulnerability has a CVSS 3.1 base score of 4.4, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2026-77955?
Check the references section for vendor advisories and patches from nlnetlabs. Update unbound to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-77955?
CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-77955 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.
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