Medium 6.3Published Apr 10, 2026

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

Updated under an hour ago (Oct 27, 2026, 6:10 AM ET)

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It affects Apache Software Foundation Apache Log4cxx and 2 other products. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for Apache Software Foundation Apache Log4cxx

Exploited in the last 30 days

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.

CVSS: 6.3 MEDIUM (v4.0, CNA)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
Weakness (CWE): CWE-116
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: apache
NVD analysis: Analyzed
Record last updated: Apr 10, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Apache Software Foundation Apache Log4cxx apache:log4cxx	before 1.7.0	CNA record
Apache Software Foundation Apache Log4cxx (Conan) apache_software_foundation:apache_log4cxx_conan (from the name)	before 1.7.0	CNA record
Apache Software Foundation Apache Log4cxx (Brew) apache_software_foundation:apache_log4cxx_brew (from the name)	before 1.7.0	CNA record
apache log4cxx apache:log4cxx	before 1.7.0	NVD

References

References

https://github.com/apache/logging-log4cxx/pull/609	patch, issue-tracking
https://logging.apache.org/security.html#CVE-2026-40023	vendor-advisory
https://logging.apache.org/cyclonedx/vdr.xml	vendor-advisory, product
https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html	related, product
https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b	vendor-advisory, mailing-list
http://www.openwall.com/lists/oss-security/2026/04/10/12	mailing-list, third-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.