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Advisory record · GHSA-h383-gmxw-35v2

Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

CVSS 6.9 MediumEPSS 0.0054 · 45th 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>=2.7, <2.25.4 || >=3.0.0-beta1, <=3.0.0-beta22.25.4
Identifiers
GHSA-h383-gmxw-35v2 · CVE-2026-34479
Weakness (CWE)
CWE-116
Tags
Published
10 Apr 2026
Updated
26 Oct 2026

Machine-written summary

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

Log4j Core (org.apache.logging.log4j:log4j-core) versions 2.7 up to but not including 2.25.4, and 3.0.0-beta1 through 3.0.0-beta2, are affected. The Log4j1XmlLayout in the Log4j 1-to-Log4j 2 bridge does not escape XML 1.0 forbidden characters, so it produces malformed XML that conforming parsers reject, which can cause downstream systems to drop or fail to index log records. The source gives few details on attacker requirements. Upgrade to version 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 0.0054, the 45th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:16 UTC First seen by agentprime
  2. 31 Oct 2026, 14:16 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.