CVE-2026-34479

MEDIUM EPSS 41.1%
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

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records. Two groups of users are affected: * Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file. * Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class. Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue. Note: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge.

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
41.1% percentile
Exploit & Patch Status
Public Exploit Known
Patch Available

Weaknesses 1

CWE-116

Affected Products 6

VendorProductVersionRange
apachelog4j*≥2.7  –  <2.25.4
apachelog4j3.0.0any
apachelog4j3.0.0any
apachelog4j3.0.0any
apachelog4j3.0.0any
apachelog4j3.0.0any

References 6

  • openwall.com http://www.openwall.com/lists/oss-security/2026/04/10/8
    Mailing List
  • github.com https://github.com/apache/logging-log4j2/pull/4078
    ExploitIssue TrackingPatch
  • lists.apache.org https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on
    Mailing List
  • logging.apache.org https://logging.apache.org/cyclonedx/vdr.xml
    Vendor Advisory
  • logging.apache.org https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html
    Mitigation
  • logging.apache.org https://logging.apache.org/security.html#CVE-2026-34479
    Vendor Advisory

Remediation

  • github.com https://github.com/apache/logging-log4j2/pull/4078
    ExploitIssue TrackingPatch