CVE-2026-4437
published 2026-03-20CVE-2026-4437: 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…
PriorityP340high7.5CVSS 3.1
AVNACLPRNUINSUCNINAH
EPSS
0.33%
24.8th percentile
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
6 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | glibc | < glibc 2.42-14 (forky) | glibc 2.42-14 (forky) |
| gnu | glibc | >= 0 < 2.42-14 | 2.42-14 |
| gnu | glibc | 2.34 – 2.43 | — |
| msrc | azl3_glibc_2.38-18_on_azure_linux_3.0 | — | — |
| msrc | cbl2_glibc_2.35-10_on_cbl_mariner_2.0 | — | — |
| the_gnu_c_library | glibc | 2.34 – 2.43 | — |
CVSS provenance
nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
osv7.5HIGH
vendor_debian7.5HIGH
vendor_redhat7.5HIGH
vendor_msrc5.9MEDIUM
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OSV
CVE-2026-4437: Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch
osv·2026-03-20·CVSS 7.5
CVE-2026-4437 [HIGH] CVE-2026-4437: Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch
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.
GHSA
GHSA-m5wq-r4r4-4qrh: Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch
ghsa_unreviewed·2026-03-20
CVE-2026-4437 [HIGH] CWE-125 GHSA-m5wq-r4r4-4qrh: Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch
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.
Red Hat
glibc: glibc: Incorrect DNS response parsing via crafted DNS server response
vendor_redhat·2026-03-20·CVSS 7.5
CVE-2026-4437 [HIGH] CWE-1286 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response
glibc: glibc: Incorrect DNS response parsing via crafted DNS server 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.
A flaw was found in glibc (the GNU C Library). When an application uses the `gethostbyaddr` or `gethostbyaddr_r` functions with a `nsswitch.conf` configuration that specifies glibc's DNS backend, a remote attacker can send a specially crafted DNS (Domain Name System) response. This crafted response can cause the application to incorrectly interpret
Microsoft
gethostbyaddr and gethostbyaddr_r may incorrectly handle DNS response
vendor_msrc·2026-03-10·CVSS 5.9
CVE-2026-4437 [HIGH] CWE-125 gethostbyaddr and gethostbyaddr_r may incorrectly handle DNS response
gethostbyaddr and gethostbyaddr_r may incorrectly handle DNS response
Mariner: Mariner
glibc: glibc
Customer Action Required: Yes
Remediation: CBL-Mariner Releases
Reference: https://learn.microsoft.com/en-us/azure/azure-linux/tutorial-azure-linux-upgrade
Debian
CVE-2026-4437: glibc - Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that sp...
vendor_debian·2026·CVSS 7.5
CVE-2026-4437 [HIGH] CVE-2026-4437: glibc - Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that sp...
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.
Scope: local
bookworm: open
bullseye: open
forky: resolved (fixed in 2.42-14)
sid: resolved (fixed in 2.42-14)
trixie: open
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response [fedora-42]
bugzilla·2026-03-23·CVSS 7.5
CVE-2026-4437 [HIGH] CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response [fedora-42]
CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response [fedora-42]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
Fixed by the following update:
https://bodhi.fedoraproject.org/updates/FEDORA-2026-cd29bb324d
Bugzilla
CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response [fedora-43]
bugzilla·2026-03-23·CVSS 7.5
CVE-2026-4437 [HIGH] CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response [fedora-43]
CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response [fedora-43]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
Fixed in glibc-2.42-11.fc43
https://bodhi.fedoraproject.org/updates/FEDORA-2026-d13513697d
Bugzilla
CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response
bugzilla·2026-03-20·CVSS 7.5
CVE-2026-4437 [HIGH] CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server response
CVE-2026-4437 glibc: glibc: Incorrect DNS response parsing via crafted DNS server 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.
Bugzilla
CVE-2025-4437 cri-o1.29: Large /etc/passwd file may lead to Denial of Service [fedora-42]
bugzilla·2025-06-26·CVSS 5.7
CVE-2025-4437 [MEDIUM] CVE-2025-4437 cri-o1.29: Large /etc/passwd file may lead to Denial of Service [fedora-42]
CVE-2025-4437 cri-o1.29: Large /etc/passwd file may lead to Denial of Service [fedora-42]
More information about this security flaw is available in the following bug:
https://bugzilla.redhat.com/show_bug.cgi?id=2375084
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This message is a reminder that Fedora Linux 42 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora Linux 42 on 2026-05-13.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
'version' of '42'.
Bugzilla
CVE-2025-4437 cri-o1.31: Large /etc/passwd file may lead to Denial of Service [fedora-42]
bugzilla·2025-06-26·CVSS 5.7
CVE-2025-4437 [MEDIUM] CVE-2025-4437 cri-o1.31: Large /etc/passwd file may lead to Denial of Service [fedora-42]
CVE-2025-4437 cri-o1.31: Large /etc/passwd file may lead to Denial of Service [fedora-42]
More information about this security flaw is available in the following bug:
https://bugzilla.redhat.com/show_bug.cgi?id=2375084
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This message is a reminder that Fedora Linux 42 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora Linux 42 on 2026-05-13.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
'version' of '42'.
Bugzilla
CVE-2025-4437 cri-o1.30: Large /etc/passwd file may lead to Denial of Service [fedora-42]
bugzilla·2025-06-26·CVSS 5.7
CVE-2025-4437 [MEDIUM] CVE-2025-4437 cri-o1.30: Large /etc/passwd file may lead to Denial of Service [fedora-42]
CVE-2025-4437 cri-o1.30: Large /etc/passwd file may lead to Denial of Service [fedora-42]
More information about this security flaw is available in the following bug:
https://bugzilla.redhat.com/show_bug.cgi?id=2375084
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This message is a reminder that Fedora Linux 42 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora Linux 42 on 2026-05-13.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
'version' of '42'.
Bugzilla
CVE-2025-4437 cri-o: Large /etc/passwd file may lead to Denial of Service [fedora-42]
bugzilla·2025-06-26·CVSS 5.7
CVE-2025-4437 [MEDIUM] CVE-2025-4437 cri-o: Large /etc/passwd file may lead to Denial of Service [fedora-42]
CVE-2025-4437 cri-o: Large /etc/passwd file may lead to Denial of Service [fedora-42]
More information about this security flaw is available in the following bug:
https://bugzilla.redhat.com/show_bug.cgi?id=2375084
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This message is a reminder that Fedora Linux 42 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora Linux 42 on 2026-05-13.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
'version' of '42'.
Pa
Wiz
CVE-2026-4437 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 10.0
CVE-2026-4437 [CRITICAL] CVE-2026-4437 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-4437 :
Wolfi vulnerability analysis and mitigation
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.
Source : NVD
## 7.5
Score
Published March 20, 2026
Severity HIGH
CNA Score 7.5
Affected Technologies
Wolfi
Chainguard
Has Public Exploit Yes
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 16.4
Exploitation Probability (EPSS) 0.1
Affected packages and libraries
glibc-langpack-f
2026-03-20
Published