CVE-2026-40023

low-risk

Published 2026-04-10

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.

Do I need to act?

0.25% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 5.3/10 Medium

NETWORK / LOW complexity

Affected Products (1)

Log4Cxx

Affected Vendors

Apache

References (6)

Issue Tracking https://github.com/apache/logging-log4cxx/pull/609

Mailing List https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b

Product https://logging.apache.org/cyclonedx/vdr.xml

Product https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html

Vendor Advisory https://logging.apache.org/security.html#CVE-2026-40023

Mailing List http://www.openwall.com/lists/oss-security/2026/04/10/12

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low-risk

Severity 21/34 · High

Exploitability 1/34 · Minimal

Exposure 5/34 · Minimal