Unbound 1.6.21.25.1: respip rewrites BOGUS DNSSEC answers as INSECURE
CVE-2026-50243 Published on July 22, 2026
'response-ip'/'rpz' can rewrite BOGUS answers instead of returning SERVFAIL
In NLnet Labs Unbound 1.6.2 up to and including 1.25.1, when Unbound is 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, the rewriting handler does not check the security status of the upstream answer and can instead rewrite a BOGUS A/AAAA answer to point to an operator's configured IP. If the validator finds an expired or otherwise invalid RRSIG on an answer whose A record falls within a 'response-ip'/RPZ configuration, the answer is still rewritten and given a hard coded security level of INSECURE. This results in the client receiving an INSECURE NOERROR reply rewritten by the operator's configured IP. A malicious actor can exploit the possible poisonous effect by spoofing a BOGUS A/AAAA answer that falls inside the operator's configured subnet rewrites. Such DNSSEC protected answers are then insecurely redirected to the operator's configured target.
Timeline
Issue reported by Qifan Zhang
NLnet Labs shares patch 30 days later.
Qifan Zhang verifies patch 3 days later.
Fixes released with version 1.25.2 41 days later.
Weakness Type
Use of Less Trusted Source
The software has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.
Products Associated with CVE-2026-50243
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Affected Versions
NLnet Labs Unbound:- Version 1.6.2 and below 1.25.2 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.