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.
Metrics
Affected Vendors & Products
No advisories yet.
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
Fri, 10 Apr 2026 18:15:00 +0000
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Fri, 10 Apr 2026 17:30:00 +0000
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Fri, 10 Apr 2026 16:00:00 +0000
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| Description | 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. | |
| Title | Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters | |
| First Time appeared |
Apache
Apache log4j 1 2 Api |
|
| Weaknesses | CWE-116 | |
| CPEs | cpe:2.3:a:apache:log4j_1_2_api:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Apache
Apache log4j 1 2 Api |
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| References |
| |
| Metrics |
cvssV4_0
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Projects
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Status: PUBLISHED
Assigner: apache
Published:
Updated: 2026-04-10T17:47:34.402Z
Reserved: 2026-03-28T14:06:31.965Z
Link: CVE-2026-34479
Updated: 2026-04-10T16:18:18.699Z
Status : Received
Published: 2026-04-10T16:16:31.270
Modified: 2026-04-10T17:17:02.403
Link: CVE-2026-34479
No data.
OpenCVE Enrichment
No data.