Improper Handling of Inconsistent Special Elements Affecting log4j:2/log4j-jcl package, versions *


Severity

Recommended
0.0
medium
0
10

Based on Red Hat Enterprise Linux security rating.

Threat Intelligence

EPSS
0.12% (31st percentile)

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  • Snyk IDSNYK-RHEL8-LOG4J-16073703
  • published15 Apr 2026
  • disclosed10 Apr 2026

Introduced: 10 Apr 2026

NewCVE-2026-34480  (opens in a new tab)
CWE-168  (opens in a new tab)

How to fix?

There is no fixed version for RHEL:8 log4j:2/log4j-jcl.

NVD Description

Note: Versions mentioned in the description apply only to the upstream log4j:2/log4j-jcl package and not the log4j:2/log4j-jcl package as distributed by RHEL. See How to fix? for RHEL:8 relevant fixed versions and status.

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 log-processing systems to drop the affected records.
  • Alternative StAX implementations (e.g., Woodstox https://github.com/FasterXML/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.

CVSS Base Scores

version 3.1