Bug 2457317 (CVE-2026-40023)

Summary: CVE-2026-40023 Apache Log4cxx: Apache Log4cxx: Log processing impairment due to unsanitized XML characters
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Apache Log4cxx. An attacker who can influence logged data can exploit this by injecting characters forbidden by the XML 1.0 specification (a standard for encoding documents) into log messages, Network Device Configuration (NDC), and Mapped Diagnostic Context (MDC) property keys and values. This results in invalid XML output, causing downstream log processing systems to drop or fail to index affected records. The primary impact is the impairment of audit trails and the detection of malicious activity, leading to a Denial of Service (DoS) for log processing.
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Bug Depends On: 2457922, 2457923    
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Description OSIDB Bzimport 2026-04-10 16:01:52 UTC 
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.