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Message-ID: <1a9db885-83c0-b06e-4867-b9f52c5d1d14@apache.org>
Date: Tue, 06 Oct 2026 19:42:55 +0000
From: Jan Friedrich <freeandnil@...che.org>
To: oss-security@...ts.openwall.com
Subject: CVE-2026-105240: Apache log4net: NUL character truncates
OutputDebugStringAppender records
Severity: moderate
CVSS 3.1: 5.3 (medium) CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Affected versions:
- Apache log4net 1.2.9 before 3.5.0
- Apache log4net 02e1e115435888485f2e28b414d267e39e799e07 before 6046fe9d7f353b49fe995361c071ec2eea8f7ef6
Description:
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.
Credit:
The Apache Software Foundation (finder)
Claude Security (tool)
Jan Friedrich (remediation developer)
References:
https://github.com/apache/logging-log4net/pull/315
https://github.com/apache/logging-log4net/commit/6046fe9d7f353b49fe995361c071ec2eea8f7ef6
https://logging.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-105240
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