CVE-2026-105239

Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net. A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use EventLogAppender 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/dc5855a0720c91590fd7a81d729ea01fdd69e000
• https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq
• http://www.openwall.com/lists/oss-security/2026/10/07/14