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.
Advisories

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Fixes

Solution

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Workaround

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History

Fri, 10 Apr 2026 18:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 10 Apr 2026 17:30:00 +0000

Type Values Removed Values Added
References

Fri, 10 Apr 2026 16:00:00 +0000

Type Values Removed Values Added
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.
Title Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility
First Time appeared Apache
Apache log4j
Weaknesses CWE-117
CWE-684
CPEs cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*
Vendors & Products Apache
Apache log4j
References
Metrics cvssV4_0

{'score': 6.9, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: apache

Published:

Updated: 2026-04-10T17:50:12.484Z

Reserved: 2026-03-28T13:17:35.586Z

Link: CVE-2026-34478

cve-icon Vulnrichment

Updated: 2026-04-10T16:18:17.528Z

cve-icon NVD

Status : Received

Published: 2026-04-10T16:16:31.070

Modified: 2026-04-10T17:17:02.237

Link: CVE-2026-34478

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses