What’s Vulnerable › Vulnerabilities

CVE-2026-105239: Apache log4net: NUL character truncates EventLogAppender records

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-06 · updated 2026-10-09
• Weakness: CWE-158

Description

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.

Affected products

• Apache Software Foundation Apache log4net: from 1.2.9 before 3.5.0 — fixed in 3.5.0

How to fix

Upgrade to a fixed version: Apache Software Foundation Apache log4net 3.5.0. Check the vendor advisory for mitigations.

References

• https://github.com/apache/logging-log4net/commit/dc5855a0720c91590fd7a81d729ea01fdd69e000
• https://github.com/apache/logging-log4net/pull/315
• https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq
• http://www.openwall.com/lists/oss-security/2026/10/07/14

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