CVE-2026-4438

Shell injection via unchecked reverse-DNS hostname

Published Mar 20, 2026 · Updated Mar 20, 2026

Improper input validation in GNU Project glibc 2.34 through 2.43 allows man-in-the-middle attackers to return invalid DNS hostnames. The getanswer_ptr function extracts reverse-DNS answers without rejecting shell metacharacters before gethostbyaddr or gethostbyaddr_r returns the hostname. Shell injection requires the DNS NSS backend, an adjacent or compromised DNS path, and an application that passes the returned hostname to a shell without guarding expansion.

CVSS severity5.4
Medium
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper input validation in GNU Project glibc 2.34 through 2.43 allows man-in-the-middle attackers to return invalid DNS hostnames. The getanswer_ptr function extracts reverse-DNS answers without rejecting shell metacharacters before gethostbyaddr or gethostbyaddr_r returns the hostname. Shell injection requires the DNS NSS backend, an adjacent or compromised DNS path, and an application that passes the returned hostname to a shell without guarding expansion.

The record

CVE
CVE-2026-4438
Published
Mar 20, 2026
Updated
Mar 20, 2026
Vendor
The GnuPG Project
Product
glibc
Classifications
CWE-20, CWE-88, T1059
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.34 <=2.43

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

The GnuPG Project · glibcversion=2.34 <=2.43

Published CVSS scores

5.4CISA-ADPCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-88Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
T1059Command and Scripting Interpreter

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo