Severity: moderate Affected versions:
- Apache Log4j Core (org.apache.logging.log4j:log4j-core) 2.21.0 before 2.25.4 - Apache Log4j Core (org.apache.logging.log4j:log4j-core) 3.0.0-beta1 through 3.0.0-beta3 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. Credit: Samuli Leinonen (finder) References: https://github.com/apache/logging-log4j2/pull/4074 https://logging.apache.org/security.html#CVE-2026-34478 https://logging.apache.org/cyclonedx/vdr.xml https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout https://logging.apache.org/ https://www.cve.org/CVERecord?id=CVE-2026-34478 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
