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CVE-2026-35501— Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.

Quick assessment

Affected
NLnet Labs Unbound
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

当 NLnet Labs 的 Unbound（版本从 1.0.1 到 1.26.1，含该版本）同时配置了根信任锚（root trust anchor）和针对某个“安全孤岛”（island-of-security）区域的额外 配置，且该孤岛区域的父级在根信任链下可被证明为不安全时，攻击者可通过伪造一条 SOA 位被清除的 NSEC 响应，诱使 Unbound 将已配置的信任孤岛视为不安全区域。 该漏洞的成因在于：Unbound 的 DNSSEC 验证器接受并缓存了该 NSEC 不安全响应，从而绕过了本应执行的 RRS

CVSS 3.7 · Low
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I. Basic Information for CVE-2026-35501

Vulnerability Information
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Vulnerability Title
Bypass of a configured island trust anchor underneath an insecure parent from an atacker-controlled NSEC record.
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
完整性检查值验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
NLnet Labs Unbound 1.0.1 ~ 1.26.2 -

II. Public POCs for CVE-2026-35501

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III. Intelligence Information for CVE-2026-35501

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Other References for CVE-2026-35501 (1)

Same Patch Batch · NLnet Labs · 2026-10-21 · 5 CVEs total

CVE-2026-97206 7.5 HIGH DNS-over-QUIC (DoQ) path-migration can lead to use-after-free on multi-threaded deployment
CVE-2026-50106 6.5 MEDIUM Possible insecure NXDOMAIN for non-existing records under a configured island trust anchor
CVE-2026-109125 5.3 MEDIUM Possible cache poisoning vulnerability via a cache side-channel exposed by 'unwanted-reply
CVE-2026-96405 5.3 MEDIUM Aggregate DNS name chained pointer decompression work leads to degradation of service.

IV. Related Vulnerabilities

Same product: Unbound
Same vendor: NLnet Labs
Same weakness: CWE-354

V. Comments for CVE-2026-35501

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