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Glibc EUVDEUVD-2026-13798

| CVE-2026-4438 MEDIUM
Improper Input Validation (CWE-20)
2026-03-20 glibc
Information Disclosure Glibc The Gnu C Library
5.4
CVSS 3.1 · Vendor: glibc
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Vulnerability Assessment

Weakness
CWE
CWE-20
OWASP Top 10:2025
A03:2021 - Injection
ASVS 5.0
V5 - Validation, Sanitization and Encoding Input validation, output encoding, parameterized queries
Impact

The risk assessment is complicated by missing CVSS scoring and EPSS data. However, the technical indicators suggest moderate real-world risk: the attack vector is network-based (DNS response manipulation requires network access or control of DNS infrastructure), privileges required are likely none or low, and user interaction is not required. The vulnerability is classified as Information Disclosure, suggesting that compromised hostname resolution could expose incorrect or sensitive hostname mappings. No active exploitation (KEV status), proof-of-concept, or widespread detection has been publicly documented. The technical impact is primarily data integrity rather than confidentiality or availability—systems receive incorrect but not exploitable hostnames. The affected product is foundational (glibc), meaning the vulnerability impacts virtually all Linux distributions and embedded systems using affected versions, increasing the scope of remediation required. The 10-version span (2.34 to 2.43) indicates a long-standing bug, suggesting low exploitation complexity but also extended exposure window. This is a moderate-priority vulnerability requiring timely patching but not critical without active exploitation evidence.
Exploit ScenarioDerived

An attacker controlling or able to influence DNS responses (via network man-in-the-middle position, DNS cache poisoning, or compromised resolver) crafts a malformed DNS hostname that violates RFC 1035 specifications. When a vulnerable glibc application calls gethostbyaddr or gethostbyaddr_r to resolve an IP address, glibc accepts and returns the invalid hostname without proper validation. The application then propagates this invalid hostname through logs, configurations, or network communications, potentially triggering further vulnerabilities in downstream systems that perform insufficient validation, or leaking information about the poisoned resolver. No public proof-of-concept code has been disclosed, and exploitation requires network-level access to manipulate DNS responses, making opportunistic attacks unlikely without specific targeting.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 20, 2026

The GNU C Library (glibc) versions 2.34 through 2.43 contain a vulnerability in the gethostbyaddr and gethostbyaddr_r functions that can return invalid DNS hostnames violating DNS specification requirements when using a configured nsswitch.conf with the DNS backend. This affects any application or system service relying on reverse DNS lookups through glibc, potentially leading to information disclosure or incorrect hostname resolution. While no CVSS score, EPSS probability, or active exploitation status has been publicly assigned, the vulnerability represents a data integrity issue in a foundational system library affecting millions of Linux systems.

RemediationAI

Upgrade glibc to version 2.44 or later, which contains the fix for invalid DNS hostname validation in the gethostbyaddr and gethostbyaddr_r functions. For Debian and Ubuntu systems, run apt-get update && apt-get upgrade libc6 to the latest patched version. For RHEL and Fedora, use yum/dnf update glibc to version 2.44 or later. For Alpine Linux, update musl-c or glibc package to the patched version. Verify the installed glibc version using ldd --version or dpkg -l | grep libc6. Until patching is complete, monitor nsswitch.conf configurations and consider restricting DNS backend usage to trusted, validated resolvers where possible. For systems unable to immediately patch, validate all reverse DNS lookups through application-level checks to ensure hostname compliance with DNS specifications before using them in security-sensitive operations.

Affected VersionsENISA

glibc 2.34 ≤2.43

Affected Packages

euvd glibc no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

The vulnerability resides in the GNU C Library (glibc), a critical component providing the C standard library and system call interfaces for POSIX-compliant operating systems. Specifically, the gethostbyaddr and gethostbyaddr_r functions perform reverse DNS lookups by querying DNS infrastructure to resolve IP addresses to hostnames. The affected versions (2.34 through 2.43, identified via CPE cpe:2.3:a:the_gnu_c_library:glibc:*:*:*:*:*:*:*:*) contain a flaw in DNS response processing when nsswitch.conf explicitly configures the DNS backend for address-to-name resolution. The root cause is classified as CWE-20 (Improper Input Validation), indicating that glibc fails to properly validate or sanitize DNS responses, allowing malformed or non-compliant DNS hostnames to be returned to callers. This violates RFC 1035 DNS naming conventions and can propagate invalid data throughout the application stack.

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Severity by source

Vendor (glibc) PRIMARY 5.4 MEDIUM
AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
SUSE MEDIUM
Red Hat 4.0 LOW

Primary rating from Vendor (glibc).

CVSS VectorVendor: glibc

Attack Vector
Adjacent
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

Lifecycle Timeline

2
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
CVE Published
Mar 20, 2026 - 19:59 nvd
MEDIUM 5.4

DescriptionCVE.org

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 result in an invalid DNS hostname being returned to the caller in violation of the DNS specification.

Executive ViewAI

Why It Matters

Organizations using the GNU C library should be aware of moderate risk from CVE-2026-4438, a input validation vulnerability rated CVSS 5.4. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and monitor for exploitation.

Business Impact: Low
Compensating Controls

Apply vendor patch. If patching is delayed: deploy WAF rules, restrict network access, enable logging.

Threat Intelligence Overview

EPSS Score
0.0%
Top 89% exploitable
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment MSRC Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Defer
Exploitation
None
System Exposure· derived
Controlled
Automatable
No
Human Impact
Low
Technical Impact
Partial

Priority Score

27
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +27
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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Same weakness CWE-20 – Improper Input Validation

View all
CVE-2021-44228 CRITICAL POC
10.0
CVE-2024-3400 CRITICAL POC
10.0
CVE-2022-47966 CRITICAL POC
9.8
CVE-2023-22515 CRITICAL POC
9.8
CVE-2009-0927 HIGH POC
8.8
CVE-2017-9791 CRITICAL POC
9.8
CVE-2017-15944 CRITICAL POC
9.8
CVE-2019-0604 CRITICAL POC
9.8

Same technique Information Disclosure

View all
CVE-2019-2725 CRITICAL POC
9.8
CVE-2021-34523 CRITICAL POC
9.0
CVE-2013-2251 CRITICAL POC
9.8
CVE-2017-5638 CRITICAL POC
9.8
CVE-2025-24813 CRITICAL POC
9.8
CVE-2025-68613 HIGH POC
8.8
CVE-2015-1701 HIGH POC
7.8
CVE-2017-0147 HIGH POC
7.5

Vendor StatusVendor

Debian

glibc
Release Status Fixed Version Urgency
bullseye vulnerable 2.31-13+deb11u11 -
bullseye (security) vulnerable 2.31-13+deb11u13 -
bookworm vulnerable 2.36-9+deb12u13 -
bookworm (security) vulnerable 2.36-9+deb12u7 -
trixie vulnerable 2.41-12+deb13u2 -
forky, sid vulnerable 2.42-13 -
(unstable) fixed (unfixed) -

SUSE

Severity: Medium
Product Status
Container rancher/elemental-channel/sl-micro:6.0-baremetal Container rancher/elemental-channel/sl-micro:6.0-base Container rancher/elemental-channel/sl-micro:6.0-kvm Container rancher/elemental-channel/sl-micro:6.0-rt Container suse/sl-micro/6.0/baremetal-iso-image:2.1.4-6.152 Container suse/sl-micro/6.0/base-iso-image:2.1.4-5.152 Container suse/sl-micro/6.0/kvm-iso-image:2.1.4-6.159 Container suse/sl-micro/6.0/rt-iso-image:2.1.4-6.151 Container suse/sl-micro/6.1/baremetal-iso-image:2.2.1-5.97 Container suse/sl-micro/6.1/base-iso-image:2.2.1-5.114 Container suse/sl-micro/6.1/kvm-iso-image:2.2.1-5.127 Container suse/sl-micro/6.1/rt-iso-image:2.2.1-5.101 Affected
Container suse/sl-micro/6.0/baremetal-os-container:2.1.3-6.158 Image SLE-Micro Image SLE-Micro-Azure Image SLE-Micro-BYOS Image SLE-Micro-BYOS-Azure Image SLE-Micro-BYOS-EC2 Image SLE-Micro-EC2 Affected
Container suse/sl-micro/6.0/base-os-container:2.1.3-7.125 Container suse/sl-micro/6.0/kvm-os-container:2.1.3-6.142 Container suse/sl-micro/6.0/rt-os-container:2.1.3-7.156 Container suse/sl-micro/6.1/baremetal-os-container:2.2.1-7.88 Container suse/sl-micro/6.1/base-os-container:2.2.1-5.112 Container suse/sl-micro/6.1/kvm-os-container:2.2.1-5.114 Container suse/sl-micro/6.1/rt-os-container:2.2.1-5.102 Image SL-Micro Image SL-Micro-Base Image SL-Micro-Base-RT Image SL-Micro-Base-RT-SelfInstall Image SL-Micro-Base-RT-encrypted Image SL-Micro-Base-SelfInstall Image SL-Micro-Base-encrypted Image SL-Micro-Base-qcow Image SL-Micro-Default Image SL-Micro-Default-SelfInstall Image SL-Micro-Default-encrypted Image SL-Micro-Default-qcow Image SLE-Micro-BYOS-GCE Image SLE-Micro-GCE Affected
Container suse/sl-micro/6.0/toolbox:13.2-9.93 Affected
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise High Performance Computing 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-4438 ADVISORY https://seclists.org/oss-sec/2026/q3/275 ADVISORY https://ubuntu.com/security/notices/USN-8611-1 ADVISORY https://vuldb.com/?id.352112 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1369/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:20999/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21019/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21039/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21069/ REF https://cert-portal.siemens.com/productcert/html/ssa-082556.html REF https://sourceware.org/bugzilla/show_bug.cgi?id=34015

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