CVE-2026-4437: gethostbyaddr and gethostbyaddr_r may incorrectly handle DNS response

mediumCVSS 5.9CVE-2026-4437

CSIRTS triage

Information disclosure

What: The gethostbyaddr and gethostbyaddr_r functions may incorrectly process DNS responses, leading to information disclosure or incorrect DNS resolution.
Who is affected: Applications using affected DNS lookup functions in vulnerable C library versions.
Urgency: Medium priority; DNS response handling issues can affect reliability and expose sensitive information.
Action: Apply C library updates addressing CVE-2026-4437 from your OS vendor.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 5.9
Published: 2026-08-06
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-4437

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-44370.33% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 25% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-4437	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

medium[UPDATE] [medium] GNU libc: Multiple vulnerabilities allow manipulation of DNS responsescert-bund
unknownUSN-8611-1: GNU C Library vulnerabilitiesubuntu

Recent advisories for gethostbyaddr and gethostbyaddr_r

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-4438: gethostbyaddr and gethostbyaddr_r return invalid DNS hostnamesmsrc · 2026-08-06