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
No CVSS.
References
Configurations
No configuration.
History
10 Apr 2026, 17:17
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
10 Apr 2026, 16:16
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-04-10 16:16
Updated : 2026-04-13 15:02
NVD link : CVE-2026-34480
Mitre link : CVE-2026-34480
CVE.ORG link : CVE-2026-34480
JSON object : View
Products Affected
No product.
CWE
CWE-116
Improper Encoding or Escaping of Output