Medium6.9Apache Software Foundation

Medium [CVE-2026-34480] Apache Log4j Core's XmlLayout https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout , in versions up to and…

This medium-severity Apache Software Foundation advisory covers CVE-2026-34480 affecting Apache Log4j, Apache Log4j Core, Log4j.

CVE-2026-34480 Published Apr 10, 2026Updated by vendor Jun 17, 2026

CVE-2026-34480

Affected products & platforms

Apache Software FoundationLog4j

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Summary

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 versions

2.25.3

Official advisory · high-confidence parse· fetched 2 months ago·verify at source

Fixed versions

2.25.4

Official advisory · high-confidence parse· fetched 2 months ago·verify at source

Mitigation

Upgrade to a fixed release: 2.25.4. That is the remediation for this advisory.

The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.

Official advisory · high-confidence parse· fetched 2 months ago·verify at source

Sources

Official and corroborating records used to build this advisory.

NVD discovery recordNVD
Independent discovery and scoring cross-reference. Vendor remediation guidance takes precedence. Discovered from the machine-readable feed https://services.nvd.nist.gov/rest/json/cves/2.0; this link opens the NVD record for CVE-2026-34480 instead of the raw feed document.
NIST National Vulnerability Database

Cross-references

Validate CVE metadata against the authoritative registries.

CVE-2026-34480NVD CVE.org MITRE

Official resources

ASF Security — reporting & CVE process
Official documentation
The Apache Software Foundation's official security page: how ASF CVEs are published and where each project's advisories live.
Apache project downloads (fixed releases)
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Official ASF download tree — fetch the fixed release named in this advisory from the project's directory.

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