Input validation error in Unbound - CVE-2026-50243
Published: July 23, 2026
Vulnerability identifier: #VU139230
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-50243
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: NLnet Labs
Affected software:
Unbound
Unbound
Detailed vulnerability description
The vulnerability allows a remote attacker to redirect DNSSEC-protected responses to an operator-configured IP.
The vulnerability exists due to improper input validation in the response-ip/RPZ-IP rewriting handler when processing rewritten upstream A/AAAA answers with invalid DNSSEC signatures. A remote attacker can spoof a BOGUS A/AAAA answer to redirect DNSSEC-protected responses to an operator-configured IP.
Exploitation requires Unbound to be configured with the respip module in front of the validator together with a response-ip redirect rule or an RPZ file with an RPZ-IP trigger.
How to mitigate CVE-2026-50243
Install security update from vendor's website.