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

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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.3% · higher than 27% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

GL

glibc · The GNU C Library

2.34 through 2.43 · source: vendor, NVD

SS

SIMATIC S7-1500 CPU 1518-4 PN/DP MFP · Siemens

V3.1.5 before V3.1.6; V3.1.5 before V3.1.6 · source: CISA

SS

SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP · Siemens

V3.1.5 before V3.1.6; V3.1.5 before V3.1.6 · source: CISA

SS

SIPLUS S7-1500 CPU 1518-4 PN/DP MFP · Siemens

V3.1.5 before V3.1.6 · source: CISA