CVE-2026-4437: Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that specifies the library's DNS back

Q: How do I fix CVE-2026-4437?

glibc: upgrade to newer than 2.43. Exact commands for each OS are on this page.

Q: Is CVE-2026-4437 being exploited?

CVE-2026-4437 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-4437 affect?

CVE-2026-4437 affects glibc. Severity is high (CVSS 7.5). Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that specifies the library's DNS backend in the GNU C Library version 2.34 to version 2.43 could, with a crafted response from the configured DNS server, result in a v

Q: How urgent is CVE-2026-4437?

Priority 43/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-4437 is a high-severity flaw (CVSS 7.5) affecting glibc. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that specifies the library's DNS backend in the GNU C Library version 2.34 to version 2.43 could, with a crafted response from the configured DNS server, result in a violation of the DNS specification that causes the application to treat a non-answer section of the DNS response as a valid answer.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 73%)
CISA exploited list	No
Weakness	CWE-125
Published	2026-03-20
Last modified	2026-07-14

Publisher (CNA): GNU C Library · Vendor: gnu

Last updated 2026-07-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-20 20:16 UTCPublished CVE record published
2026-07-14 13:18 UTCUpdated Record last modified

gnu glibc UPGRADE

Affected: >= 2.34 and <= 2.43

Fixed in: newer than 2.43

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy glibc || rpm -q glibc || glibc --version

2. UPGRADE to newer than 2.43 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade glibc

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade glibc

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:20597] Moderate: glibc security update 2026-06-30

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-4437?

glibc: upgrade to newer than 2.43. Exact commands for each OS are on this page.

Is CVE-2026-4437 being exploited?

CVE-2026-4437 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-4437 affect?

CVE-2026-4437 affects glibc. Severity is high (CVSS 7.5). Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that specifies the library's DNS backend in the GNU C Library version 2.34 to version 2.43 could, with a crafted response from the configured DNS server, result in a v

How urgent is CVE-2026-4437?

Priority 43/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

glibc vulnerabilities

Related CVEs

CVE-2026-6238 MEDIUM 6.5 MITIGATE The deprecated functions ns_printrrf, ns_printrr and fp_nquery in the GNU C Library version 2.0.1 to version 2
CVE-2026-5435 HIGH 7.3 MITIGATE The deprecated functions ns_printrrf, ns_printrr and fp_nquery in the GNU C Library version 2.2 and newer fail
CVE-2026-4438 MEDIUM 5.4 UPGRADE Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that specifies the library's DNS back
CVE-2026-4046 HIGH 7.5 UPGRADE The iconv() function in the GNU C Library versions 2.43 and earlier may crash due to an assertion failure when

References

← Back to latest CVEs