CVE-2026-34478

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

MEDIUM 6.9

At a glance

Source: NVD
EPSS: EPSS 0.97 % · percentile 62 (2026-10-28)
State: PUBLISHED
Published: 2026-04-10 15:40 UTC
Updated: 2026-04-10 17:50 UTC
Assigner: apache
NVD status: Analyzed

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.

Weaknesses (CWE)

CWE-684 — Incorrect Provision of Specified Functionality
CWE-117 — Improper Output Neutralization for Logs

References

Scores

Version	Score	Vector	Scored by
CVSS 4.0	MEDIUM 6.9	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N	apache
CVSS 4.0	MEDIUM 6.9	CVSS: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/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X	NVD · security@apache.org (Secondary)
CVSS 3.1	HIGH 7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N	NVD · nvd@nist.gov (Primary)

Advisories

GHSA-445c-vh5m-36rj — Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility

European references

ENISA EUVD · EUVD-2026-21408
GCVE · GCVE-0-2026-34478

CERT-FR advisories

CERTFR-2026-AVI-1385 — Multiples vulnérabilités dans les produits VMware · cert.ssi.gouv.fr
CERTFR-2026-AVI-1256 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-1206 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-1165 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-1121 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-1049 — Multiples vulnérabilités dans Oracle MySQL · cert.ssi.gouv.fr
CERTFR-2026-AVI-1032 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-0986 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-0958 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-0920 — Multiples vulnérabilités dans Oracle Weblogic · cert.ssi.gouv.fr
CERTFR-2026-AVI-0810 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-0698 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
CERTFR-2026-AVI-0627 — Multiples vulnérabilités dans les produits Splunk · cert.ssi.gouv.fr

Affected configurations (NVD CPE)

cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:* ≥ 2.21.0 < 2.25.4
cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:beta3:*:*:*:*:*:*

Affected products

Product	Versions
Apache Software Foundation · Apache Log4j Core	affected 2.21.0 < 2.25.4 ; affected 3.0.0-beta1 ≤ 3.0.0-beta3

Sources

Source	Licence
CVE List (CVEProject cvelistV5)	CVE Program Terms of Use
EPSS (FIRST.org)	FIRST — attribution requested
ENISA EUVD	ENISA — reproduction authorised, source acknowledged
CERT-FR (ANSSI)	Licence Ouverte / Etalab 2.0
NVD (NIST) via fkie-cad/nvd-json-data-feeds	Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD