GHSA-445c-vh5m-36rj
Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility
At a glance
- Published
- Updated
- CVE
- CVE-2026-34478
- CVSS_V4
- 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
Description
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. Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly: * 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. * 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. 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 packages
| Package | Versions |
|---|---|
| Maven · org.apache.logging.log4j:log4j-core | introduced 2.21.0, fixed 2.25.4 |
| Maven · org.apache.logging.log4j:log4j-core | introduced 3.0.0-beta1, last affected 3.0.0-beta3 |
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-34478 ADVISORY
- https://github.com/apache/logging-log4j2/pull/4074 WEB
- https://github.com/apache/logging-log4j2 PACKAGE
- https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt WEB
- https://logging.apache.org/cyclonedx/vdr.xml WEB
- https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout WEB
- https://logging.apache.org/security.html#CVE-2026-34478 WEB
- http://www.openwall.com/lists/oss-security/2026/04/10/7 WEB
Sources
| Source | Licence |
|---|---|
| OSV.dev | CC-BY 4.0 — GitHub Advisory Database |