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Vulnerabilities

Vulnerability · 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 inje…

Published Apr 10, 2026 · catalog updated Jun 17, 2026 · Apache

Check if you run it

No confirmed exploitation is on record for CVE-2026-34478. EPSS is 1.19%. Act only if a listed version of Apache is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
1.19%
Remediation
Advisory link
Affected products
cpe apache/log4j

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe apache/log4j3.0.0

How to fix CVE-2026-34478

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-34478. EPSS is 1.19%. Act only if a listed version of Apache is installed.

Which versions are affected?

Compare what you have installed with 3.0.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-117; CWE-684. EPSS 1.19%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Jun 17, 2026 · NIST NVD

    Updated

    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

  2. Oct 15, 2026 · Apache Software Foundation

    Detected

    Named on the public Apache Software Foundation page.

Sources

  • Apache Software FoundationVendor advisoryCVE-2026-34478

    CVE-2026-34478 is named on the public Apache Software Foundation page.

    logging.apache.org
  • CVE.orgVulnerability recordCVE-2026-34478

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-34478

    30-day exploitation probability 1.2%

    first.org
  • NIST NVDVulnerability recordCVE-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 distinc

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.