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CVE-2026-40023EXPLOITEDPATCHED
apache software foundation · apache log4cxx

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

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.

Affected Products

VendorProductVersions
apache software foundationapache log4cxx0, 0, 0

References

  • https://github.com/apache/logging-log4cxx/pull/609(patch)
  • https://logging.apache.org/security.html#CVE-2026-40023(vendor-advisory)
  • https://logging.apache.org/cyclonedx/vdr.xml(vendor-advisory)
  • https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html(related)
  • https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b(vendor-advisory)

Related News (1 articles)

Tier C
VulDB3h ago
CVE-2026-40023 | Apache Log4cxx up to 1.6.x escape output
→ No new info (linked only)
CISA KEV❌ No
Actively exploited✅ Yes
Patch available
1.7.0
CWECWE-116
PublishedApr 10, 2026
Last enriched2h agov2
Trending Score40
Source articles1
Independent1
Info Completeness8/14
Missing: cvss, epss, kev, exploit, iocs, mitre_attack

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Related CVEs (5)

NONECVE-2026-34480EXP
Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters
Trending: 61
CRITICALCVE-2026-34477EXP
Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowing hostname verification bypass
Trending: 61
NONECVE-2026-34479EXP
Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
Trending: 60
NONECVE-2026-34478
Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility
Trending: 41
NONECVE-2026-34481EXP
Apache Log4j JSON Template Layout: Improper serialization of non-finite floating-point values in JsonTemplateLayout
Trending: 40

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Verification

State: unverified
Confidence: 0%

Vulnerability Timeline

CVE Published
Apr 10, 2026
Discovered by ZDM
Apr 10, 2026
Updated: affectedVersions, severity, activelyExploited
Apr 10, 2026
Actively Exploited
Apr 10, 2026
Patch Available
Apr 10, 2026

Version History

v2
Last enriched 2h ago
v2Tier C2h ago

Updated affected versions to include 1.6.x and changed severity to HIGH, with the vulnerability now actively exploited.

affectedVersionsseverityactivelyExploited
via VulDB
v12h ago

Initial creation