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.
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)
|
History
06 May 2026, 18:21
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://github.com/apache/logging-log4j2/pull/4078 - Exploit, Issue Tracking, Patch | |
| References | () https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on - Mailing List | |
| References | () https://logging.apache.org/cyclonedx/vdr.xml - Vendor Advisory | |
| References | () https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html - Mitigation | |
| References | () https://logging.apache.org/security.html#CVE-2026-34479 - Vendor Advisory | |
| References | () http://www.openwall.com/lists/oss-security/2026/04/10/8 - Mailing List | |
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 7.5 |
| First Time |
Apache log4j
Apache |
|
| CPE | 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:*:*:*:*:*:*:*:* cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:* cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:* |
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 : 2026-05-06 18:21
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