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CVE-2026-35501low3.7

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

Impact

Unbound versions 1.0.1 to 1.26.1 are vulnerable to a bypass of a configured island trust anchor when an attacker-controlled NSEC record is used. An attacker with a forged NSEC reply can trick Unbound into treating the trust island as insecure. This occurs due to improper validation of the NSEC response.

Summarized by @cf/meta/llama-3.3-70b-instruct-fp8-fast. Verify details against the original sources.

What to do

This issue is fixed starting with version 1.26.2

NLnet Labs guidance

Affected packages

This source has no supported package-version data for matching. You can read the advisory here, but this record alone cannot power a dependency check.

Affected products

Vendor version evidence. Product records are separate from automatic dependency matching.

NLnet Labs · NLnet Labs

Unbound

1 range
NLnet Labs version evidence

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affected

1.0.1 → before 1.26.2

semver versions

unaffected

unknown

Other versions: unaffected

Original source description

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.

Inside the record

Evidence available

Package identity · not supplied
Version evidence
Remediation guidance
Weakness classification
Additional publishers

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Original records

CVE-2026-35501

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Underlying weaknesses

The source’s classification of what caused the vulnerability.

CWE-354 ↗

CWE-354: Improper Validation of Integrity Check Value

NLnet Labs

Related →
Contributing organizations · 2
NLnet Labs

Assigning organization

2026-10-21
CISA-ADP

Additional data publisher

2026-10-29

What changed

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References

1 sources
www.nlnetlabs.nl/downloads/unbound/CVE-2026-35501.txt
vendor-advisoryNLnet Labs