CVE-2026-34478: Apache Log4j Core Log Injection Vulnerability
MODERATECVE-2026-34478 is a MODERATE log injection vulnerability (CWE-684: Incorrect Provision of Specified Functionality) affecting Apache Log4j Core libraries in the Maven ecosystem. The issue involves log injection in `rfc5424layout` due to silent configuration incompatibility. Remediation is available by upgrading affected packages to version 2.25.4.
CVE-2026-34478 at a Glance
How to Fix CVE-2026-34478
To remediate this vulnerability, upgrade all affected Apache Log4j Core 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-core</artifactId>
<version>2.25.4</version>
</dependency><dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</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-2026-34478, 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 Core 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-684: Incorrect Provision of Specified Functionality, where the code does not function according to its published specifications, potentially leading to incorrect usage. In Apache Log4j Core, 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-2026-34478 Affected Apache Log4j Core Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
org.apache.logging.log4j:log4j-core
|
Maven |
≥ 2.21.0
< 2.25.4
|
2.25.4
|
|
org.apache.logging.log4j:log4j-core
|
Maven |
≥ 3.0.0-beta1
≤ 3.0.0-beta3
|
|
References
Frequently Asked Questions
What is CVE-2026-34478?
Which Apache Log4j Core versions are affected?
What version fixes CVE-2026-34478?
Is log4j-core affected?
What CWE is associated with CVE-2026-34478?
How can I check Maven dependencies for CVE-2026-34478?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-445c-vh5m-36rj",
"modified" : "2026-04-14T00:13:29Z",
"published" : "2026-04-10T18:31:17Z",
"aliases" : [ "CVE-2026-34478" ],
"summary" : "Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility",
"details" : "Apache Log4j Core's [`Rfc5424Layout`](https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout), in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevant configuration attributes.\n\nTwo distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly:\n\n * The `newLineEscape` attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output.\n * The `useTlsMessageFormat` attribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping.\n\nUsers of the `SyslogAppender` are not affected, as its configuration attributes were not modified.\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.",
"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-core"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.21.0"
}, {
"fixed" : "2.25.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Maven",
"name" : "org.apache.logging.log4j:log4j-core"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "3.0.0-beta1"
}, {
"last_affected" : "3.0.0-beta3"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34478"
}, {
"type" : "WEB",
"url" : "https://github.com/apache/logging-log4j2/pull/4074"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/apache/logging-log4j2"
}, {
"type" : "WEB",
"url" : "https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt"
}, {
"type" : "WEB",
"url" : "https://logging.apache.org/cyclonedx/vdr.xml"
}, {
"type" : "WEB",
"url" : "https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout"
}, {
"type" : "WEB",
"url" : "https://logging.apache.org/security.html#CVE-2026-34478"
}, {
"type" : "WEB",
"url" : "http://www.openwall.com/lists/oss-security/2026/04/10/7"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-117", "CWE-684" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-04-14T00:13:29Z",
"nvd_published_at" : "2026-04-10T16:16:31Z"
}
}