CVE-2026-34479

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/apache/logging-log4j2/pull/4078	Exploit Issue Tracking Patch
https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on	Mailing List
https://logging.apache.org/cyclonedx/vdr.xml	Vendor Advisory
https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html	Mitigation
https://logging.apache.org/security.html#CVE-2026-34479	Vendor Advisory
http://www.openwall.com/lists/oss-security/2026/04/10/8	Mailing List

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:apache:log4j::::::::
	cpe:2.3:a:apache:log4j:3.0.0:alpha1::::::
	cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc1::::::
	cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc2::::::
	cpe:2.3:a:apache:log4j:3.0.0:beta1::::::
	cpe:2.3:a:apache:log4j:3.0.0:beta2::::::

History

No history.

Information

Published : 2026-04-10 16:16

Updated : 2026-06-17 10:39

NVD link : CVE-2026-34479

Mitre link : CVE-2026-34479

CVE.ORG link : CVE-2026-34479

JSON object : View

Products Affected

apache

log4j

CWE

CWE-116

Improper Encoding or Escaping of Output

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