CVE-2026-105240

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender are affected. This issue affects Apache log4net: from 1.2.9 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Score

CVSS 3.1 5.3 Medium

Status

Analyzed - security@apache.org

Published

2026-10-06

Last modified

2026-10-09

Weaknesses

CWE-158

Affected products

• Log4net (Apache)
• Apache Log4net (Apache Software Foundation)

References

• https://github.com/apache/logging-log4net/pull/315
• https://github.com/apache/logging-log4net/commit/6046fe9d7f353b49fe995361c071ec2eea8f7ef6
• https://lists.apache.org/thread.html/gyw2d4ppy82t1vlpdknkfd1nmzp21z17
• http://www.openwall.com/lists/oss-security/2026/10/07/18