CVE-2026-34480

A flaw was found in Apache Log4j Core. The XmlLayout component, responsible for formatting log messages into XML, does not properly remove or replace characters that are not allowed in XML 1.0. When log messages or diagnostic information contain these forbidden characters, the resulting XML output becomes invalid. This can lead to two main issues: either systems processing these logs will fail to read the affected records, or the logging process itself will stop delivering events, both resulting in a denial of service for logging operations.

This flaw in Apache Log4j Core's XmlLayout component can lead to a denial of service in logging operations when log messages contain characters forbidden by the XML 1.0 specification. Systems processing these logs may fail to read records or the logging process may cease event delivery, impacting monitoring and auditing capabilities in affected Red Hat products. Red Hat products in their default configurations will be able to automatically recover, but some log messages may be lost.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.