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TI-2026-78543 Aliases CVE-2026-35501GHSA-mh74-9w87-h7vx

Trust island bypass in NLnet Labs Unbound via forged NSEC replies

Priority LOW 16CWE-354Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
—
Confidentiality · integrity · availability
None · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

NLnet Labs Unbound from 1.0.1 before 1.26.2 is affected when it is configured with both a root trust anchor and an additional trust anchor for a secure island zone whose parent is provably insecure. The DNSSEC validator accepts and caches a forged NSEC response with the SOA bit cleared, skipping RRSIG validation (CWE-354). A remote attacker who can send forged DNS replies can make Unbound treat the configured trust island as insecure.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00111 1st percentileScored 2026-11-07
Fix Fixed Unbound (NLnet Labs): 1.26.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
NLnet LabsUnbound1.0.1 to before 1.26.21.26.2Patch availableCNA
  • Unbound VendorNLnet Labs Affected 1.0.1 to before 1.26.2 Fixed in 1.26.2 Patch available CNA

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*——NLNETLABS
  • cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* Versions — — ·NLNETLABS

Remediation

Update NLnet Labs Unbound to version 1.26.2, which is the fixed version.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

  • Fix · CNA Unbound (NLnet Labs) Fixed in 1.26.2

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    NLnet Labs Unbound 1.26.2

    5 records Highest priority Priority LOW 5 LOW

    Other records, highest priority first

    • TI-2026-78586 Unbound DoQ path migration use-after-free on multi-threaded deploymentsPriority LOW 39
    • TI-2026-78584 Unbound resolver lacks aggregate limit on DNS compression pointersPriority LOW 30
    • TI-2026-78546 Unbound NXDOMAIN denial for island trust anchor under insecure parentPriority LOW 28
    Show all 5 records →

Timeline

  1. 2026-10-21 Threatist record created from CVE-2026-35501
  2. 2026-10-21 Alias added: GHSA-mh74-9w87-h7vx
  3. 2026-10-29 CISA SSVC decision points changed

References

Advisory 1

  • TI-2026-25690 Possible arbitrary code execution during DNSSEC validation CVSS 4.0CRITICAL 9.1
  • TI-2026-56302 Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY CVSS 4.0CRITICAL 9.1
  • TI-2026-31146 Crash during DNSSEC validation of malicious content CVSS 4.0HIGH 8.7
  • TI-2026-31135 Heap overflow with multiple NSID, COOKIE, PADDING EDNS options CVSS 4.0HIGH 8.7
  • TI-2026-36436 Routinator crashes on specifically crafted RRDP XML files CVSS 4.0HIGH 8.7
  • TI-2026-36433 Routinator exits when accepting an incoming HTTP or RTR connection fails CVSS 4.0HIGH 8.7
See all 96 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences