---
id: CVE-2026-105244
title: >-
  Improper Encoding or Escaping of Output vulnerability in the
  RemoteSyslogAppender of Apache log4net.


  Every character outside visible ASCII and space was removed from the record
  instead of being escaped, so non-ASCII text and control cha…
summary: >-
  Improper Encoding or Escaping of Output vulnerability in the
  RemoteSyslogAppender of Apache log4net.


  Every character outside visible ASCII and space was removed from the record
  instead of being escaped, so non-ASCII text and control cha…
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-116
vendor: apache
product: log4net
affected:
  - 'log4net >= 1.2.12, < 3.5.0'
patched:
  - log4net 3.5.0
published: '2026-10-06'
updated: '2026-10-09'
sourceUpdated: '2026-10-09T15:18:44.677'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-105244'
references:
  - url: >-
      https://github.com/apache/logging-log4net/commit/77717061b20d4346b6c0ce6b54643d85fb348bc7
    label: security@apache.org
  - url: 'https://github.com/apache/logging-log4net/pull/315'
    label: security@apache.org
  - url: 'https://lists.apache.org/thread.html/q7649hhdodthoqw8jsjgtnb4m8qfy6d6'
    label: security@apache.org
  - url: 'http://www.openwall.com/lists/oss-security/2026/10/07/19'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - cve.org
epss: 0.00823
epssPercentile: 0.57157
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-07T14:50:00.691563Z'
ingestedAt: '2026-10-06T20:16:42.474Z'
---

## Overview

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.

## Affected

- `log4net >= 1.2.12, < 3.5.0`

## Remediation

Upgrade past the affected range:

- `log4net 3.5.0`