XML Injection Affecting log4j-slf4j package, versions *


Severity

Recommended
0.0
medium
0
10

Based on Red Hat Enterprise Linux security rating.

Threat Intelligence

Social Trends
EPSS
0.54% (41st percentile)

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  • Snyk IDSNYK-RHEL9-LOG4JSLF4J-16070113
  • published15 Apr 2026
  • disclosed10 Apr 2026

Introduced: 10 Apr 2026

CVE-2026-34479  (opens in a new tab)
CWE-91  (opens in a new tab)

How to fix?

There is no fixed version for RHEL:9 log4j-slf4j.

NVD Description

Note: Versions mentioned in the description apply only to the upstream log4j-slf4j package and not the log4j-slf4j package as distributed by RHEL. See How to fix? for RHEL:9 relevant fixed versions and status.

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.

Two groups of users are affected:

  • Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file.
  • Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class.

Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.

Note: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge.

CVSS Base Scores

version 3.1