Improper Verification of Cryptographic Signature in Unbound - CVE-2026-35501
Published: October 21, 2026
Vulnerability identifier: #VU156692
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-35501
CWE-ID: CWE-347
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass DNSSEC validation and cause a configured trust-anchor zone to be treated as insecure.
The vulnerability exists due to improper cryptographic signature verification in the Unbound DNSSEC validator when processing NSEC replies at a configured trust anchor apex. A remote attacker can supply a forged NSEC reply with the SOA bit cleared to have it accepted and cached without RRSIG validation, causing the configured trust island to be treated as insecure when both a root trust anchor and an additional island-of-security trust anchor are configured and the island's parent is provably insecure under the root chain.
Affected software
Unbound
How to mitigate CVE-2026-35501
Install security update from vendor's website.
Unbound - update to 1.26.2