Bug 2457313 (CVE-2026-34479)

Summary:	CVE-2026-34479 org.apache.logging.log4j/log4j-1.2-api: Apache Log4j 1-to-Log4j 2 bridge: Log processing denial of service due to improper XML escaping
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	asoldano, bbaranow, bmaxwell, bstansbe, chfoley, dlofthou, gmalinko, istudens, ivassile, iweiss, janstey, jkoehler, lphiri, mosmerov, msvehla, nwallace, pberan, pdelbell, pesilva, pjindal, pmackay, rgodfrey, rstancel, rstepani, smaestri, swoodman, thjenkin, vdosoudi
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Apache Log4j 1-to-Log4j 2 bridge. The Log4j1XmlLayout component fails to properly escape characters forbidden by the XML 1.0 standard. This improper handling of characters results in malformed XML output, which can cause downstream log processing systems to drop or fail to index affected records. The primary consequence is a denial of service for log analysis, potentially hindering security monitoring and incident response.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2457912, 2457914, 2457911, 2457913
Bug Blocks:

Description OSIDB Bzimport 2026-04-10 16:01:35 UTC

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.