CVE-2026-50251
5.3 · MEDIUMOverview
CVE-2026-50251 is a medium-severity vulnerability affecting nlnetlabs unbound. It was published on July 22, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
In NLnet Labs Unbound up to and including version 1.25.1, when 'unwanted-reply-threshold' is enabled (set to any value greater than zero), glue records of 0.0.0.0/::0 can short-circuit Unbound, on systems that can direct such traffic, by issuing DNS queries and receiving seemingly unwanted replies since the remote IP does not match the original source IP of 0.0.0.0/::0. This behavior keeps on looping for the glue records and pushing the counter to the configured 'unwanted-reply-threshold' that triggers a defensive cache clear. A malicious actor who controls a delegation that returns in-bailiwick glue of 0.0.0.0/::0 can drive the counter to the limit of 'unwanted-reply-threshold' to the threshold and trigger a cache clean of the message and rrset caches; at will, indefinitely, without sending a single spoofed packet. The iterator uses the 0.0.0.0/::0 glue, and a system that can route this (e.g., Linux kernel routes the datagram over loopback), Unbound's own listener answers from 127.0.0
Remediation
Check the references section for vendor advisories and patches from nlnetlabs. Update unbound to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| nlnetlabs | unbound | >= 0, < 1.25.2 | Affected |
Frequently Asked Questions
What is CVE-2026-50251?
CVE-2026-50251 is a medium-severity vulnerability affecting nlnetlabs unbound. It was published on July 22, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).
How severe is CVE-2026-50251?
This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-50251?
Check the references section for vendor advisories and patches from nlnetlabs. Update unbound to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-50251?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-50251 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
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