CVE-2026-50243 'response-ip'/'rpz' can rewrite BOGUS answers instead of returning SERVFAIL
Attackers can bypass DNSSEC validation by spoofing BOGUS answers that are insecurely rewritten by response-ip or RPZ rules in Unbound.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-50243?
CVE-2026-50243 is a medium-severity vulnerability in Nlnetlabs Unbound, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-348
Which versions are affected by CVE-2026-50243?
It affects 1 product.
Products include Nlnetlabs Unbound.
How do I fix CVE-2026-50243?
Upgrade to a fixed version.
Is CVE-2026-50243 being exploited?
There is no known exploitation of CVE-2026-50243 in the wild and no public exploit code.
Other vulnerabilities in Nlnetlabs Unbound
- CVE-2026-81642 Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY
- CVE-2026-33278 Possible arbitrary code execution during DNSSEC validation
- CVE-2026-42944 Heap overflow with multiple NSID, COOKIE, PADDING EDNS options
- CVE-2026-42959 Crash during DNSSEC validation of malicious content
- CVE-2026-82717 CNAME synthesis could lead to heap corruption
Sources
Also known as ALPINE-CVE-2026-50243, AZL-92988, DEBIAN-CVE-2026-50243, ECHO-47eb-2c54-a673, GHSA-vqq3-g95x-fpmr, UBUNTU-CVE-2026-50243.