VulnerabilityAnalyzed

CVE-2026-34478

MEDIUM 6.9EPSS 0.97%

Does this matter?

Lower severity and a low EPSS score (0.97%). Track it; it rarely justifies an emergency change on its own.

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 4.0: 6.9 MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
EPSS: 0.97% probability · 60th percentile
CISA KEV: Not listed
Weakness: CWE-117, CWE-684
Affected: apache/log4j
Source: security@apache.org

References

https://github.com/apache/logging-log4j2/pull/4074Issue Tracking, Patch
https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwtMailing List, Vendor 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 List, Third Party Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.