CVE-2026-34478
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.
EPSS 0.03% · 10.6th percentile
Risk Scores
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache Log4j Core | 2.21.0, 3.0.0-beta1 |
Timeline
- Apr 10, 2026 CVE Published
- Apr 10, 2026 PoC Published
- Apr 14, 2026 CVE Updated
- Apr 14, 2026 Security Advisory
- May 18, 2026 EPSS Score
- May 19, 2026 EPSS Score
- May 20, 2026 EPSS Score
- May 21, 2026 EPSS Score
- May 22, 2026 EPSS Score
- May 23, 2026 EPSS Score
- May 24, 2026 EPSS Score
- May 25, 2026 EPSS Score
References
- https://github.com/apache/logging-log4j2/pull/4074 patch
- https://logging.apache.org/security.html#CVE-2026-34478 vendor-advisory
- https://logging.apache.org/cyclonedx/vdr.xml vendor-advisory
- https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout url
- https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt vendor-advisory
- http://www.openwall.com/lists/oss-security/2026/04/10/7 url
- https://advisory.splunk.com/advisories/SVD-2026-0512 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0513 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0509 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0510 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0505 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0515 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0507 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0506 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0508 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0504 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0514 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0516 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0501 advisory
- https://advisory.splunk.com/advisories/SVD-2026-0503 advisory
…and 2 more