CVE-2026-34479: Apache Log4j 1 to Log4j 2 bridge Silent Log Event Loss Vulnerability
MODERATECVE-2026-34479 is a MODERATE silent log event loss vulnerability (CWE-116: Improper Encoding or Escaping of Output) affecting Apache Log4j 1 to Log4j 2 bridge libraries in the Maven ecosystem. The issue involves silent log event loss in log4j1xmllayout due to unescaped xml 1.0 forbidden characters. Remediation is available by upgrading affected packages to version 2.25.4.
CVE-2026-34479 at a Glance
How to Fix CVE-2026-34479
To remediate this vulnerability, upgrade all affected Apache Log4j 1 to Log4j 2 bridge dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-1.2-api</artifactId>
<version>2.25.4</version>
</dependency><dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-1.2-api</artifactId>
<version>Latest secure release</version>
</dependency>Run the following command in your project directory to verify that all resolved dependencies use the patched release:
mvn dependency:tree -Dincludes=org.apache.logging.log4jHow to Check if You Are Affected
To determine whether your Java application is affected by CVE-2026-34479, inspect your build dependencies using the Maven Dependency Plugin:
mvn dependency:tree -Dincludes=org.apache.logging.log4jAnalyze the terminal output to locate any version of Apache Log4j 1 to Log4j 2 bridge in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.25.4), your application is affected.
Note: The mvn dependency:tree -Dincludes=org.apache.logging.log4j command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-116: Improper Encoding or Escaping of Output, where the product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. as a result, the intended structure of the message is not preserved. In Apache Log4j 1 to Log4j 2 bridge, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-34479 Affected Apache Log4j 1 to Log4j 2 bridge Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
org.apache.logging.log4j:log4j-1.2-api
|
Maven |
≥ 2.7
< 2.25.4
|
2.25.4
|
|
org.apache.logging.log4j:log4j-1.2-api
|
Maven |
≥ 3.0.0-beta1
≤ 3.0.0-beta2
|
|
References
Frequently Asked Questions
What is CVE-2026-34479?
Which Apache Log4j 1 to Log4j 2 bridge versions are affected?
What version fixes CVE-2026-34479?
Is log4j-1.2-api affected?
What CWE is associated with CVE-2026-34479?
How can I check Maven dependencies for CVE-2026-34479?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-h383-gmxw-35v2",
"modified" : "2026-04-14T00:10:59Z",
"published" : "2026-04-10T18:31:18Z",
"aliases" : [ "CVE-2026-34479" ],
"summary" : "Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters",
"details" : "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.\n\nTwo groups of users are affected:\n\n* Those using `Log4j1XmlLayout` directly in a Log4j Core 2 configuration file.\n* Those using the Log4j 1 configuration compatibility layer with `org.apache.log4j.xml.XMLLayout` specified as the layout class.\n\nUsers are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version `2.25.4`, which corrects this issue.\n\n> [!NOTE]\n> The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the\n> [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.",
"severity" : [ {
"type" : "CVSS_V4",
"score" : "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"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Maven",
"name" : "org.apache.logging.log4j:log4j-1.2-api"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.7"
}, {
"fixed" : "2.25.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Maven",
"name" : "org.apache.logging.log4j:log4j-1.2-api"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "3.0.0-beta1"
}, {
"last_affected" : "3.0.0-beta2"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34479"
}, {
"type" : "WEB",
"url" : "https://github.com/apache/logging-log4j2/pull/4078"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/apache/logging-log4j2"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on"
}, {
"type" : "WEB",
"url" : "https://logging.apache.org/cyclonedx/vdr.xml"
}, {
"type" : "WEB",
"url" : "https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html"
}, {
"type" : "WEB",
"url" : "https://logging.apache.org/security.html#CVE-2026-34479"
}, {
"type" : "WEB",
"url" : "http://www.openwall.com/lists/oss-security/2026/04/10/8"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-116" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-04-14T00:10:59Z",
"nvd_published_at" : "2026-04-10T16:16:31Z"
}
}