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CVE-2026-34478

Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

Published: Apr 10, 2026Updated: Apr 24, 2026 Sources: CVE List NVD BDUCWE-117
NVD MITRE
7.5CVSSHIGH
EPSS Score
0.8%
Top 47.3%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:HA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:HIntegrity
High
A:NAvailability
None
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Weaknesses

CWE-117CWE-684

Affected Products

Apache Log4j CoreApache Software Foundation
Mixed
Web & CMS Plugins / cms-core
log4japache
LibraryLibrary
OSS Libraries / generic-library
apache software foundationoss-projectUSWeb & CMS Pluginsaka apache foundation
apacheoss-projectUSWeb & CMS Pluginsaka apache http server, apache httpd

Exploitability

Official Patch Available

References

https://github.com/apache/logging-log4j2/pull/4074
github.com
https://logging.apache.org/security.html#CVE-2026-34478
logging.apache.org
https://logging.apache.org/cyclonedx/vdr.xml
logging.apache.org
and 6 more references View all →

Timeline

Published
Apr 10, 2026
Last Updated
Apr 24, 2026

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