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.
Problem types
CWE-684 Incorrect Provision of Specified Functionality
CWE-117 Improper Output Neutralization for Logs
Product status
2.21.0 (maven) before 2.25.4
3.0.0-beta1 (maven)
Timeline
| 2025-12-25: | Vulnerability reported by Samuli Leinonen |
| 2026-03-10: | Candidate patch shared internally by Piotr P. Karwasz |
| 2026-03-24: | Fix shared publicly by Piotr P. Karwasz as pull request #4074 |
| 2026-03-25: | Fix verified by reporter |
| 2026-03-28: | Log4j 2.25.4 released |
Credits
Samuli Leinonen
References
www.openwall.com/lists/oss-security/2026/04/10/7
github.com/apache/logging-log4j2/pull/4074
logging.apache.org/security.html
logging.apache.org/cyclonedx/vdr.xml
logging.apache.org/log4j/2.x/manual/layouts.html
lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt