CVE-2026-105240: Apache LOG4NET

Medium severity, CVSS 5.3. EPSS: 0.8% chance of exploitation in the next 30 days.

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.

Affected products

• Apache LOG4NET: from 1.2.9, before 3.5.0 (fixed in 3.5.0)

Published 2026-10-06. Last modified 2026-10-09.