Vulnerability · Published Apr 10, 2026 · Assigned by apache
CVE-2026-34479Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
Medium 6.9
In plain English
A medium-severity security flaw in Apache Log4j 1 to Log4j 2 bridge from Apache Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | apache-log4j2 | no fix listed | DEBIAN-CVE-2026-34479 |
| Debian:13 | apache-log4j2 | no fix listed | DEBIAN-CVE-2026-34479 |
| Debian:14 | apache-log4j2 | no fix listed | DEBIAN-CVE-2026-34479 |
| Maven | org.apache.logging.log4j:log4j-core | 2.25.4 | GHSA-h383-gmxw-35v2 |
| Maven | org.apache.logging.log4j:log4j-core | no fix listed | GHSA-h383-gmxw-35v2 |
| Ubuntu:22.04:LTS | apache-log4j1.2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:24.04:LTS | apache-log4j1.2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:25.10 | apache-log4j1.2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:26.04:LTS | apache-log4j1.2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:26.10 | apache-log4j1.2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:22.04:LTS | apache-log4j2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:24.04:LTS | apache-log4j2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:25.10 | apache-log4j2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:26.04:LTS | apache-log4j2 | no fix listed | UBUNTU-CVE-2026-34479 |
| Ubuntu:26.10 | apache-log4j2 | no fix listed | UBUNTU-CVE-2026-34479 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache Log4j 1 to Log4j 2 bridge | 2.7 – before 2.25.43.0.0-alpha1 – through 3.0.0-beta2 |
Weakness: CWE-116 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
References
- https://github.com/apache/logging-log4j2/pull/4078 patch
- https://logging.apache.org/security.html#CVE-2026-34479 vendor-advisory
- https://logging.apache.org/cyclonedx/vdr.xml vendor-advisory
- https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html related
- https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on vendor-advisory
- http://www.openwall.com/lists/oss-security/2026/04/10/8