---
id: CVE-2026-105243
title: >-
  Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.


  Long messages were truncated to a fixed size that exceeds what the Windows
  Event Log accepts once the log and source names are counted, and the event log
  then…
summary: >-
  Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.


  Long messages were truncated to a fixed size that exceeds what the Windows
  Event Log accepts once the log and source names are counted, and the event log
  then…
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-778
vendor: Apache Software Foundation
product: log4net
affected:
  - log4net >= 1.2.9 < 3.5.0
  - >-
    log4net >= 02e1e115435888485f2e28b414d267e39e799e07 <
    28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed
published: '2026-10-06'
updated: '2026-10-06'
sourceUpdated: '2026-10-06T20:17:16.167'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-105243'
references:
  - url: >-
      https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed
    label: security@apache.org
  - url: 'https://github.com/apache/logging-log4net/pull/315'
    label: security@apache.org
  - url: 'https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp'
    label: security@apache.org
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-06T20:16:42.475Z'
---

## Overview

Insufficient Logging vulnerability in the EventLogAppender of Apache log4net.

Long messages were truncated to a fixed size that exceeds what the Windows Event Log accepts once the log and source names are counted, and the event log then stored nothing and reported nothing. A party whose data reaches a log message could suppress the whole record by making it long enough. 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.