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

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.

Published Mar 20, 2026Updated Jul 14, 2026Sources: cvelistV5, glibc

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Unreported

no source claims exploitation

EPSS

chance of exploitation in 30 days

Affects

the gnu c library

4 products listed

CVSS base

7.5

HIGH

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Affected scope

The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.

Vendors (2)

the gnu c library siemens

Products (4)

glibcsimatic s7 1500 cpu 1518 4 pn dp mfpsimatic s7 1500 cpu 1518f 4 pn dp mfpsiplus s7 1500 cpu 1518 4 pn dp mfp

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
7.5	CVSS 3.1	HIGH	—	—	cvelistV5

Weakness & attack patterns

CWE-125

References

2 on the record

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

Elsewhere on this site

the gnu c libraryevery CVE for this vendor
siemensevery CVE for this vendor
CWE-125other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.