CVE-2026-34478: CWE-684 Incorrect Provision of Specified Functionality in Apache Software Foundation Apache Log4j Core
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.
AI Analysis
Technical Summary
The vulnerability in Apache Log4j Core's Rfc5424Layout affects versions 2.21.0 through 2.25.3. It arises from undocumented renames of the newLineEscape and useTlsMessageFormat configuration attributes. The newLineEscape attribute rename disables newline escaping for TCP framing (RFC 6587), enabling CRLF injection in logs. The useTlsMessageFormat attribute rename causes TLS framing (RFC 5425) to downgrade silently to unframed TCP without newline escaping. This impacts users who configure Rfc5424Layout directly, but not those using SyslogAppender. The vendor has addressed this issue in version 2.25.4.
Potential Impact
The vulnerability allows CRLF injection in log output when using stream-based syslog services with Rfc5424Layout configured directly. This can lead to log injection attacks, potentially affecting log integrity and security monitoring. There is no indication of privilege escalation or remote code execution. Users of SyslogAppender are not impacted.
Mitigation Recommendations
Users should upgrade Apache Log4j Core to version 2.25.4, which corrects the configuration attribute renaming issues and restores proper newline escaping and TLS framing behavior. No other mitigations are indicated by the vendor. Patch status is confirmed by the vendor advisory recommending upgrade to 2.25.4.
CVE-2026-34478: CWE-684 Incorrect Provision of Specified Functionality in Apache Software Foundation Apache Log4j Core
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in Apache Log4j Core's Rfc5424Layout affects versions 2.21.0 through 2.25.3. It arises from undocumented renames of the newLineEscape and useTlsMessageFormat configuration attributes. The newLineEscape attribute rename disables newline escaping for TCP framing (RFC 6587), enabling CRLF injection in logs. The useTlsMessageFormat attribute rename causes TLS framing (RFC 5425) to downgrade silently to unframed TCP without newline escaping. This impacts users who configure Rfc5424Layout directly, but not those using SyslogAppender. The vendor has addressed this issue in version 2.25.4.
Potential Impact
The vulnerability allows CRLF injection in log output when using stream-based syslog services with Rfc5424Layout configured directly. This can lead to log injection attacks, potentially affecting log integrity and security monitoring. There is no indication of privilege escalation or remote code execution. Users of SyslogAppender are not impacted.
Mitigation Recommendations
Users should upgrade Apache Log4j Core to version 2.25.4, which corrects the configuration attribute renaming issues and restores proper newline escaping and TLS framing behavior. No other mitigations are indicated by the vendor. Patch status is confirmed by the vendor advisory recommending upgrade to 2.25.4.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- apache
- Date Reserved
- 2026-03-28T13:17:35.586Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69d91fde1cc7ad14dacba27b
Added to database: 4/10/2026, 4:05:50 PM
Last enriched: 4/10/2026, 4:21:30 PM
Last updated: 4/11/2026, 5:50:09 AM
Views: 3
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