Vulnerability
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NLow exploitation likelihood — defer if no other signals fire.
No VEX statements published for CVE-2026-34478. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.
Total impact on non-trivial mission systems