CVE-2026-105244: CWE-116 Improper Encoding or Escaping of Output in Apache Software Foundation Apache log4net
Description
CVE-2026-105244 is a medium severity vulnerability in Apache log4net's RemoteSyslogAppender where improper encoding or escaping of output causes non-ASCII and control characters to be removed from log records. This can cause distinct values to appear identical in logs, potentially misleading log analysis. The issue affects versions from 1.2.12 up to but not including 3.5.0. Upgrading to version 3.5.0 resolves the vulnerability.
CVSS v3.1
Score 5.3medium
Affected software
Apache Software Foundation
Apache log4net
Apache Software Foundation
Apache log4net
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in Apache log4net's RemoteSyslogAppender involves improper encoding or escaping of output, specifically removing every character outside visible ASCII and space instead of escaping them. This causes non-ASCII text and control characters such as tabs to disappear from log records without notice. An attacker or any party whose data is logged could exploit this to make distinct values appear identical, for example, a username containing a zero-width space could be logged as 'admin'. This affects Apache log4net versions >=1.2.12 and <3.5.0. The issue is fixed in version 3.5.0.
Potential Impact
The vulnerability does not impact confidentiality or availability but can affect the integrity of log data by making distinct logged values appear identical. This could mislead administrators or automated systems relying on logs for auditing or security monitoring, potentially hiding malicious activity or causing confusion in log analysis.
Mitigation Recommendations
Users should upgrade Apache log4net to version 3.5.0 or later, where this issue is fixed. No other mitigations are indicated or required.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- apache
- Date Reserved
- 2026-10-04T16:22:18.416Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6ac5544a2cdf04f656d9e12d
Added to database: 10/06/2026, 20:04:26 UTC
Last enriched: 10/06/2026, 20:18:57 UTC
Last updated: 10/06/2026, 20:19:15 UTC
Views: 3
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