← Vulnerability feed

Vulnerability record · CVE-2026-40023 · published 10 April 2026

CVE-2026-40023: Apache log4cxx vulnerability

Apache · Log4cxx

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.

6.3 CVSS 4.0 Medium EPSS 0.98% · top 39.2% CWE-116 · CWE-116
6.3CVSS 4.0 base score
0.98%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References
17 Jun 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/apache/logging-log4cxx/pull/609 Issue TrackingPatch
https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b Mailing ListVendor Advisory
https://logging.apache.org/cyclonedx/vdr.xml Product
https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html Product
https://logging.apache.org/security.html#CVE-2026-40023 Vendor Advisory
http://www.openwall.com/lists/oss-security/2026/04/10/12 Mailing ListThird Party Advisory

Track CVE-2026-40023 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

8.8CVE-2023-31038Apache log4cxx sql injection vulnerabilitySQL injection in Log4cxx when using the ODBC appender to send log messages to a database.  No fields sent to the database were properly escaped for S…EPSS 1.6%6.3CVE-2025-54813Apache log4cxx vulnerabilityImproper Output Neutralization for Logs vulnerability in Apache Log4cxx. When using JSONLayout, not all payload bytes are properly escaped. If an att…EPSS 1.3%2.1CVE-2025-54812Apache log4cxx vulnerabilityImproper Output Neutralization for Logs vulnerability in Apache Log4cxx. When using HTMLLayout, logger names are not properly escaped when writing ou…EPSS 1.2%7.8CVE-2026-20245Cisco Catalyst SD-WAN CLI command injection via crafted file uploadCisco Catalyst SD-WAN Controller, Manager and Validator fail to properly validate user-supplied input in the CLI, allowing an authenticated local att…KEVEPSS 25%analysed9.1CVE-2024-38475Apache HTTP Server mod_rewrite improper escaping enables code executionApache HTTP Server 2.4.59 and earlier has an improper output escaping flaw in mod_rewrite. Substitutions in server context that use a backreference o…KEVEPSS 100%analysed9.8CVE-2022-42948Cobalt Strike UI HTML injection leads to remote code executionCobalt Strike 4.7.1 fails to escape HTML tags rendered in its Swing UI components. Crafted HTML injected into that UI can execute code in the Cobalt …KEVEPSS 2.7%analysed6.1CVE-2022-24682Zimbra Collaboration Suite Calendar stored XSS via unescaped HTML attributesThe Calendar feature in Zimbra Collaboration Suite 8.8.x before 8.8.15 patch 30 (update 1) fails to escape HTML placed inside element attributes, all…KEVEPSS 31%analysed

Source: NIST National Vulnerability Database (record CVE-2026-40023), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.