---
id: CVE-2026-105239
title: >-
  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 i…
summary: >-
  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 i…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'
cwe:
  - CWE-158
vendor: Apache Software Foundation
product: log4net
affected:
  - log4net >= 1.2.9 < 3.5.0
  - >-
    log4net >= 02e1e115435888485f2e28b414d267e39e799e07 <
    dc5855a0720c91590fd7a81d729ea01fdd69e000
published: '2026-10-06'
updated: '2026-10-06'
sourceUpdated: '2026-10-06T20:17:15.630'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-105239'
references:
  - url: >-
      https://github.com/apache/logging-log4net/commit/dc5855a0720c91590fd7a81d729ea01fdd69e000
    label: security@apache.org
  - url: 'https://github.com/apache/logging-log4net/pull/315'
    label: security@apache.org
  - url: 'https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq'
    label: security@apache.org
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-06T19:58:19.202424Z'
ingestedAt: '2026-10-06T20:16:42.468Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.