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Fencer Vulns
low 3.7

CVE-2026-35501 json

Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.

published 2026-10-21 18 d ago modified 2026-10-29 10 d ago also EUVD-2026-107151

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 1%
public exploits
0
none known

Summary

When NLnet Labs Unbound 1.0.1 up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor with a forged NSEC reply with the SOA bit cleared can trick Unbound to treat the configured trust island as insecure. This happens because the DNSSEC validator in Unbound accepts and caches the NSEC insecure response bypassing the RRSIG validation that the validator was supposed to do. The acceptance of the NSEC record at the trust anchor apex was allowed due to and old fix for type DS and NSEC queries from clients when trust anchor for that name existed.

Patch / fix

  • NLnet Labs Unbound 1.26.2
  • unbound Debian 13 1.26.2-0+deb13u1
  • unbound Debian 14 1.26.2-1

debian advisories DEBIAN-CVE-2026-35501

  • unbound openSUSE Tumbleweed 1.26.2-1.1

opensuse advisories openSUSE-SU-2026:12257-1

  • unbound Azure Linux 3.0 1.26.2-1

azure linux advisories AZL-109821

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
10 d ago

Exploit prediction

0.11% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected products

  • NLnet Labs Unbound

Classification

Weakness
  • CWE-354 Improper Validation of Integrity Check Value

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.