CVE-2026-4438: gethostbyaddr and gethostbyaddr_r return invalid DNS hostnames

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-20 · updated 2026-07-14
Weakness: CWE-20

Description

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 result in an invalid DNS hostname being returned to the caller in violation of the DNS specification.

Affected products

GNU C Library (glibc): from 2.34 through 2.43

References

https://sourceware.org/bugzilla/show_bug.cgi?id=34015
https://cert-portal.siemens.com/productcert/html/ssa-082556.html

Get alerted when CVE-2026-4438 or the next vulnerability affects your stack