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CVE-2026-40023— Apache Log4cxx, Apache Log4cxx (Conan), Apache Log4cxx (Brew): Silent log event loss in XMLLayout due to unescaped XML 1.0 forbidden characters

Quick assessment

Affected
Apache Software Foundation Apache Log4cxx
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Apache Log4cxx是美国阿帕奇（Apache）基金会的一个以 Apache log4j 为模式的 C++ 日志框架。 Apache Log4cxx 1.7.0之前版本存在安全漏洞，该漏洞源于XMLLayout未清理XML 1.0规范禁止的字符，可能导致日志记录丢失。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.98% · P61

Possible ATT&CK Techniques 1 AI

T1070 · Indicator Removal
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I. Basic Information for CVE-2026-40023

Vulnerability Information
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Vulnerability Title
Apache Log4cxx, Apache Log4cxx (Conan), Apache Log4cxx (Brew): Silent log event loss in XMLLayout due to unescaped XML 1.0 forbidden characters
Source: CVE Program / CVE List V5
Vulnerability Description
Apache Log4cxx's XMLLayout https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html , in versions before 1.7.0, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in log messages, NDC, and MDC property keys and values, producing invalid XML output. Conforming XML parsers must reject such documents with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records. An attacker who can influence logged data can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4cxx 1.7.0, which fixes this issue.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
对输出编码和转义不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Apache Log4cxx 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Apache Log4cxx是美国阿帕奇（Apache）基金会的一个以 Apache log4j 为模式的 C++ 日志框架。 Apache Log4cxx 1.7.0之前版本存在安全漏洞，该漏洞源于XMLLayout未清理XML 1.0规范禁止的字符，可能导致日志记录丢失。
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

Vendor Product Affected Versions CPE Subscribe
Apache Software Foundation Apache Log4cxx 0 ~ 1.7.0 cpe:2.3:a:apache:log4cxx:*:*:*:*:*:*:*:*
Apache Software Foundation Apache Log4cxx (Conan) 0 ~ 1.7.0 -
Apache Software Foundation Apache Log4cxx (Brew) 0 ~ 1.7.0 -

II. Public POCs for CVE-2026-40023

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III. Intelligence Information for CVE-2026-40023

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Patches & Fixes for CVE-2026-40023 (1)

Mailing List Discussions for CVE-2026-40023 (1)

Vendor Pages for CVE-2026-40023 (1)

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

CVE-2026-40021 Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescap
CVE-2026-34481 Apache Log4j JSON Template Layout: Improper serialization of non-finite floating-point val
CVE-2026-34480 Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden c
CVE-2026-34479 Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescape
CVE-2026-34478 Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibil
CVE-2026-34477 Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowin
CVE-2026-39304 Apache ActiveMQ Client, Apache ActiveMQ Broker, Apache ActiveMQ All, Apache ActiveMQ: Inco

IV. Related Vulnerabilities

Same product: Apache Log4cxx
Same vendor: Apache Software Foundation
Same weakness: CWE-116

V. Comments for CVE-2026-40023

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