CVE-2026-34478

MEDIUM EPSS 53.0%
Published Apr 10, 20262mo ago · Modified Jun 17, 20262w ago
6.9 CVSS 4.0
Medium
Find Similar
Published Apr 10, 2026 2mo ago
Last Modified Jun 17, 2026 2w ago

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 Details

Base Score
6.9
Exploitability
—
Impact
—
Vector string
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
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
53.0% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 2

CWE-117
CWE-684

Affected Products 4

VendorProductVersionRange
apachelog4j*≥2.21.0  –  <2.25.4
apachelog4j3.0.0any
apachelog4j3.0.0any
apachelog4j3.0.0any

References 6

  • openwall.com http://www.openwall.com/lists/oss-security/2026/04/10/7
    Mailing ListThird Party Advisory
  • github.com https://github.com/apache/logging-log4j2/pull/4074
    Issue TrackingPatch
  • lists.apache.org https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt
    Mailing ListVendor Advisory
  • logging.apache.org https://logging.apache.org/cyclonedx/vdr.xml
    Product
  • logging.apache.org https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout
    Technical Description
  • logging.apache.org https://logging.apache.org/security.html#CVE-2026-34478
    Vendor Advisory

Remediation

  • github.com https://github.com/apache/logging-log4j2/pull/4074
    Issue TrackingPatch