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Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden charactersGHSA-3pxv-7cmr-fjr4

Fix: apache/logging-log4j2#4077

GHSA-3pxv-7cmr-fjr4 is a CWE-116 vulnerability in org.apache.logging.log4j:log4j-core. A fix is available for org.apache.logging.log4j:log4j-core — see the affected versions and patch details below.

Also known asCVE-2026-34480
Published
Updated
Affected
2 pkgs
Patched
1 / 2
Exploits
None indexed
Exploitation data as of Nov 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-3pxv-7cmr-fjr4.

EPSS Exploitation Probability

via FIRST.org ↗
1.1%probability of exploitation in next 30 days
Lower Risk+0.02%
Lower risk than most CVEs65th percentile — riskier than 65% of all scored CVEsHighest risk
0.00%0.56%1.12%1.69%0.2%1.1%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected
☕org.apache.logging.log4j:log4j-core☕org.apache.logging.log4j:log4j-core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

Apache Log4j Core's XmlLayout, in versions up to and including 2.25.3, fails to sanitize characters forbidden by the XML 1.0 specification, producing invalid XML output whenever a log message or MDC value contains such characters.

The impact depends on the StAX implementation in use:

  • JRE built-in StAX: Forbidden characters are silently written to the output, producing malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream log-processing systems to drop the affected records.
  • Alternative StAX implementations (e.g., Woodstox, a transitive dependency of the Jackson XML Dataformat module): An exception is thrown during the logging call, and the log event is never delivered to its intended appender, only to Log4j's internal status logger.

Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.

Affected Packages

2 total 1 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.apache.logging.log4j:log4j-core≥ 2.0-alpha1&&< 2.25.42.25.4org.apache.logging.log4j:log4j-core:2.25.4
☕Mavenorg.apache.logging.log4j:log4j-core≥ 3.0.0-alpha1No fix

Affected Products

1 product · 7 configurations
Application
log4japache
≥ 2.0 && < 2.25.4
1 version
3.0.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.apache.logging.log4j:log4j-core to 2.25.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3pxv-7cmr-fjr4 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This flaw in Apache Log4j Core's XmlLayout component can lead to a denial of service in logging operations when log messages contain characters forbidden by the XML 1.0 specification. Systems processing these logs may fail to read records or the logging process may cease event delivery, impacting monitoring and…

Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Source: Red Hat security advisory for GHSA-3pxv-7cmr-fjr4 (CC BY 4.0)
ProductFixed inAdvisory
HawtIO HawtIO 4.4.0log4j-coreRHSA-2026:25089
Red Hat AMQ Broker 7.13.6log4j-coreRHSA-2026:66545
Red Hat AMQ Broker 7.14.1log4j-coreRHSA-2026:66488
Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16log4j-coreRHSA-2026:37390
Red Hat Data Grid 8.6.1log4j-coreRHSA-2026:22619
Streams for Apache Kafka 2.9.4log4j-coreRHSA-2026:34608
Streams for Apache Kafka 3.2.1log4j-coreRHSA-2026:54435
Red Hat Offline Knowledge Portal 1.2.13offline-knowledge-portal/rhokp-rhel9:1779996999RHSA-2026:21773

Frequently Asked Questions

Apache Log4j Core's [`XmlLayout`](https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout), in versions up to and including 2.25.3, fails to sanitize characters forbidden by the [XML 1.0 specification](https://www.w3.org/TR/xml/#charsets), producing invalid XML output whenever a log message or MDC value contains such characters. The impact depends on the StAX implementation in use: * **JRE built-in StAX**: Forbidden characters are silently written to the output, producing malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream
O3 Security · Impact-Aware SCA

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