CVE-2026-34478

HighCVSS 7.5/10Last modified Jun 17, 2026

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.

Metrics

CVSS 3.1 7.5/10CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Weakness enumeration

CWE-117 CWE-684

Affected software

No affected versions have been published.

Timeline

Published: Apr 10, 2026
Last modified: Jun 17, 2026
NVD status: Analyzed

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