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CVE-2026-34479— Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

EPSS 0.15% · P36
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I. Basic Information for CVE-2026-34479

Vulnerability Information
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Vulnerability Title
Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
Source: NVD (National Vulnerability Database)
Vulnerability 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.
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
对输出编码和转义不恰当
Source: NVD (National Vulnerability Database)
Vulnerability Title
Apache Log4j 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Apache Log4j是美国阿帕奇（Apache）基金会的一款基于Java的开源日志记录工具。 Apache Log4j存在安全漏洞，该漏洞源于Log4j1XmlLayout未能转义XML 1.0标准禁止的字符，可能产生格式错误的XML输出。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

VendorProductAffected VersionsCPESubscribe
Apache Software FoundationApache Log4j 1 to Log4j 2 bridge 2.7 ~ 2.25.4 cpe:2.3:a:apache:log4j_1_2_api:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-34479

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III. Intelligence Information for CVE-2026-34479

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Same Patch Batch · Apache Software Foundation · 2026-04-10 · 8 CVEs total

CVE-2026-40023Apache Log4cxx, Apache Log4cxx (Conan), Apache Log4cxx (Brew): Silent log event loss in XM
CVE-2026-40021Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescap
CVE-2026-34481Apache Log4j JSON Template Layout: Improper serialization of non-finite floating-point val
CVE-2026-34480Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden c
CVE-2026-34478Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibil
CVE-2026-34477Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowin
CVE-2026-39304Apache ActiveMQ Client, Apache ActiveMQ Broker, Apache ActiveMQ All, Apache ActiveMQ: Inco

IV. Related Vulnerabilities

Same vendor: Apache Software Foundation
Same weakness: CWE-116

V. Comments for CVE-2026-34479

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