CVE-2026-4438 The GNU C Library CVE debrief

Who should care

Users of GNU C library version 2.34 to version 2.43 who rely on the gethostbyaddr or gethostbyaddr_r functions with a configured nsswitch.conf that specifies the library's DNS backend should be aware of this vulnerability. This includes operators, platform administrators, vulnerability management teams, and security teams who manage or use affected systems.

Technical summary

The GNU C library's DNS backend is vulnerable to an issue where calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf could result in an invalid DNS hostname being returned. This occurs in versions 2.34 to 2.43 of the library. The vulnerability is a result of the library's handling of DNS responses, which can lead to a violation of the DNS specification. Affected users should consider applying patches or updates to GNU C library versions 2.34 to 2.43.

Defensive priority

Medium priority should be given to patching or mitigating this vulnerability, especially for systems that rely heavily on DNS resolution.

Recommended defensive actions

• Review and update nsswitch.conf configurations to ensure secure DNS backend usage
• Consider applying patches or updates to GNU C library versions 2.34 to 2.43
• Monitor DNS resolution for anomalies
• Implement compensating controls for DNS resolution
• Review relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-03-20T20:16:49.623Z and was last modified on 2026-07-14T13:18:58.247Z. The NVD entry is currently Modified. This information is based on the NVD entry and the CVE record. The vulnerability affects GNU C library versions 2.34 to 2.43. The gethostbyaddr and gethostbyaddr_r functions are impacted when used with a configured nsswitch.conf that specifies the library's DNS backend. Evidence of exploitation or attack vectors is not currently available. However, defenders should verify DNS resolution configurations and monitor for anomalies.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.