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

Severity: high (CVSS 7.5 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-125

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, 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.

Affected products

GNU C Library (glibc): from 2.34 through 2.43

References

https://sourceware.org/bugzilla/show_bug.cgi?id=34014
https://cert-portal.siemens.com/productcert/html/ssa-082556.html

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