CVE-2026-35501 — Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.1% (30-day exploitation probability)+0
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Nlnetlabs Unbound).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 3.7 | CVSS 3.1 | Low | 2.2 | 1.4 | sep@nlnetlabs.nl via NIST National Vulnerability Database |
| 3.7 | CVSS 3.1 | Low | — | — | GitHub, Inc. via GitHub Security Advisories |
| 3.7 | CVSS 3.1 | Low | — | — | NLnet Labs via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N (score shown at the top: sep@nlnetlabs.nl) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 21, 2026 → Oct 27, 2026 · 7 reading(s) · max 0.11%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Timeline
What happened to this CVE, newest first.
- 2026
- Source status changed · Received → Awaiting Analysis
- Affected products added · nlnet labs/unbound
- Record published
- CVSS changed · 3.7
- Source status changed · → Received
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 21, 2026 – Oct 22, 2026
- 1× Official description updated · Oct 21, 2026 – Oct 21, 2026
References
3 on the record
Elsewhere on this site
Related CVEs (same products)
- High CVE-2026-97206 DNS-over-QUIC (DoQ) path-migration can lead to use-after-free on multi-threaded deployments. 6d
- Medium CVE-2026-96405 Aggregate DNS name chained pointer decompression work leads to degradation of service. 6d
- Medium CVE-2026-50106 Possible insecure NXDOMAIN for non-existing records under a configured island trust anchor underneath an insecure parent. 6d
- Medium CVE-2026-109125 Possible cache poisoning vulnerability via a cache side-channel exposed by 'unwanted-reply-threshold' 6d
- High CVE-2026-81634 Possible heap buffer overflow during DNSSEC canonicalization Sep 16, 2026
- Critical CVE-2026-81642 Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY Sep 16, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No CISA SSVC assessment.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-35501 is "Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.", rated Low. It affects Unbound (Nlnetlabs); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 3.7 describes technical severity. EPSS 0.11% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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