Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility
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.
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-34478US | high7.5 | — | ||
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 CR… | ||||
references
External citations — patches, advisories, analysis.
- http://www.openwall.com/lists/oss-security/2026/04/10/7WEB
- https://github.com/apache/logging-log4j2PACKAGE
- https://github.com/apache/logging-log4j2/pull/4074WEB
- https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwtWEB
- https://logging.apache.org/cyclonedx/vdr.xmlWEB
- https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424LayoutWEB
- https://logging.apache.org/security.html#CVE-2026-34478WEB
- https://nvd.nist.gov/vuln/detail/CVE-2026-34478ADVISORY
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