---
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
product: log4net
affected:
  - 'log4net >= 1.2.9, < 3.5.0'
patched:
  - log4net 3.5.0
published: '2026-10-06'
updated: '2026-10-09'
sourceUpdated: '2026-10-09T15:26:03.430'
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
  - url: 'http://www.openwall.com/lists/oss-security/2026/10/07/17'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - cve.org
epss: 0.00807
epssPercentile: 0.56638
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-07T14:49:30.641089Z'
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.

## Affected

- `log4net >= 1.2.9, < 3.5.0`

## Remediation

Upgrade past the affected range:

- `log4net 3.5.0`