Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility
Apache Log4j Core's 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.
Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly:
- The
newLineEscapeattribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output. - The
useTlsMessageFormatattribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping.
Users of the SyslogAppender are not affected, as its configuration attributes were not modified.
Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | org.apache.logging.log4j:log4j-core | >= 2.21.0, < 2.25.4, >= 3.0.0-beta1, <= 3.0.0-beta3 | 2.25.4 |
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-34478
- https://github.com/apache/logging-log4j2/pull/4074
- https://github.com/apache/logging-log4j2
- https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt
- https://logging.apache.org/cyclonedx/vdr.xml
- https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout
- https://logging.apache.org/security.html#CVE-2026-34478
- http://www.openwall.com/lists/oss-security/2026/04/10/7
- CVSS 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- Weakness (CWE)
CWE-117, CWE-684- Platform
- Java / Kotlin (Maven)
- Package
org.apache.logging.log4j:log4j-core- Disclosed
- 10.04.2026
- Updated
- 11.10.2026 13:20
Sources and licenses
OSV / GitHub Advisory Database - GHSA-445c-vh5m-36rj - CC BY 4.0
Vulnerability history: org.apache.logging.log4j:log4j-core
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 11
- First → latest
- 01.2020 04.2026
- Without a fix
- 0
- Exploited in attacks
- 2
Severity breakdown
- Critical 3
- High 2
- Medium 5
- Low 1
Disclosures per year
- 2020: 2
- 2021: 3
- 2022: 1
- 2023: 1
- 2024: 0
- 2025: 1
- 2026: 3
-
Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility this entry
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