Vulnerability · Published Jul 22, 2026 · Assigned by NLnet Labs
CVE-2026-50243'response-ip'/'rpz' can rewrite BOGUS answers instead of returning SERVFAIL
Medium 6.3
In plain English
A medium-severity security flaw in Unbound from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 1% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.22 | unbound | 1.25.2-r0 | ALPINE-CVE-2026-50243 |
| Alpine:v3.23 | unbound | 1.25.2-r0 | ALPINE-CVE-2026-50243 |
| Alpine:v3.24 | unbound | 1.25.2-r0 | ALPINE-CVE-2026-50243 |
| Debian:12 | unbound | no fix listed | DEBIAN-CVE-2026-50243 |
| Debian:13 | unbound | 1.26.1-0+deb13u1 | DEBIAN-CVE-2026-50243 |
| Debian:14 | unbound | 1.25.2-1 | DEBIAN-CVE-2026-50243 |
| Ubuntu:22.04:LTS | unbound | no fix listed | UBUNTU-CVE-2026-50243 |
| Ubuntu:24.04:LTS | unbound | no fix listed | UBUNTU-CVE-2026-50243 |
| Ubuntu:26.04:LTS | unbound | no fix listed | UBUNTU-CVE-2026-50243 |
| Ubuntu:26.10 | unbound | no fix listed | UBUNTU-CVE-2026-50243 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| NLnet Labs | Unbound | 1.6.2 – before 1.25.2 |
Weakness: CWE-348 · Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50243.txt vendor-advisory