Vulnerability 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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Apache | Log4J | >= 2.21.0, < 2.25.4 |
Related Weaknesses (CWE)
References
- https://github.com/apache/logging-log4j2/pull/4074Issue TrackingPatch
- https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwtMailing ListVendor Advisory
- https://logging.apache.org/cyclonedx/vdr.xmlProduct
- https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424LayoutTechnical Description
- https://logging.apache.org/security.html#CVE-2026-34478Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/04/10/7Mailing ListThird Party Advisory
FAQ
What is CVE-2026-34478?
CVE-2026-34478 is a vulnerability with a CVSS score of 7.5 (HIGH). 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 ...
How severe is CVE-2026-34478?
CVE-2026-34478 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-34478?
Check the references section above for vendor advisories and patch information. Affected products include: Apache Log4J.