Home/CVE/Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions
CVE

CVE-2026-34478

Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions

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.

HIGH · CVSS 7.5 EPSS 0.00034
Schedule remediation
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules0 YARA rules0
⬡

Weakness Classification

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

Affected Products & Versions

2
apache log4j>= 2.21.0 and < 2.25.4
apache log4jall versions
▤

Affected Packages

1
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Maven org.apache.logging.log4j:log4j-core MODERATE fixed in 2.25.4
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Scoring & Timeline

7.5
HIGH · CVSS v3.1 · security@apache.org
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD10 Apr 2026 · 04:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
yes
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

2
rhsaRHSA-2026:22619Important
rhsaRHSA-2026:21773Important
🔗

References & Sources

6
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
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
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