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Advisory record · GHSA-3pxv-7cmr-fjr4

Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters

CVSS 6.9 MediumEPSS 0.011 · 64th percentile

Published by the GitHub Advisory Database at 10 Apr 2026, 18:31 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
org.apache.logging.log4j:log4j-coreMaven>=2.0-alpha1, <2.25.4 || >=3.0.0-alpha1, <=3.0.0-beta32.25.4
Identifiers
GHSA-3pxv-7cmr-fjr4 · CVE-2026-34480
Weakness (CWE)
CWE-116
Tags
Published
10 Apr 2026
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Apache Log4j Core versions 2.0-alpha1 up to 2.25.3, and 3.0.0-alpha1 through 3.0.0-beta3, fail to escape XML 1.0 forbidden characters in XmlLayout output, so a log message or MDC value containing such characters produces invalid XML. Depending on the StAX implementation, the affected records may be silently written as malformed XML that downstream systems drop, or the logging call may throw an exception so the event never reaches its appender. Users should upgrade to Apache Log4j Core 2.25.4.

Written 2 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
6.9 Medium 4.0 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N CNA (apache)
  • CISA KEV Not listed.
  • EPSS 0.011, the 64th percentile, on 7 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:17 UTC First seen by agentprime
  2. 31 Oct 2026, 14:17 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.