CVE-2026-40023

Name: CVE-2026-40023
Creator: NVD / NIST
Published: 2026-04-10T16:16:32.6+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.3/10EPSS 0.50%

Last modified Jun 17, 2026

CVE-2026-40023 is a medium-severity vulnerability rated 6.3/10 on the CVSS scale. 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.. EPSS estimates a 0.50% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS 4.0

6.3/10

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:X/V:X/RE:X/U:X

EPSS Probability

0.50%

38.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-116

Affected Software

Vendor	Product	Versions
Apache	Log4cxx	< 1.7.0

References

https://github.com/apache/logging-log4cxx/pull/609Issue Tracking, Patch
https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8bMailing List, Vendor Advisory
https://logging.apache.org/cyclonedx/vdr.xmlProduct
https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.htmlProduct
https://logging.apache.org/security.html#CVE-2026-40023Vendor Advisory
http://www.openwall.com/lists/oss-security/2026/04/10/12Mailing List, Third Party Advisory

Timeline

Published: Apr 10, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-40023?

How severe is CVE-2026-40023?

CVE-2026-40023 has a CVSS score of 6.3/10 (MEDIUM severity). The EPSS model estimates a 0.50% probability of exploitation in the next 30 days.

How do I fix CVE-2026-40023?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-40023?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST