CVE-2026-105242: CWE-755 Improper Handling of Exceptional Conditions in Apache Software Foundation Apache log4net
Description
CVE-2026-105242 is a medium severity vulnerability in Apache log4net affecting versions from 1.2.11 up to but not including 3.5.0. It involves improper handling of exceptional conditions in the aspnet-request pattern converter. When request parameters trigger ASP.NET request validation errors, the logging layout throws an exception causing the appender to discard the entire log event. This allows a sender to suppress logging of their own requests. The issue only affects applications running on ASP.NET for .NET Framework that use the %aspnet-request layout pattern. Upgrading to version 3.5.0 resolves the issue.
CVSS v3.1
Score 5.3medium
Affected software
Apache Software Foundation
Apache log4net
Apache Software Foundation
Apache log4net
Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability in Apache log4net (CVE-2026-105242) arises from improper handling of exceptional conditions in the aspnet-request pattern converter. Specifically, when request parameters cause ASP.NET request validation to fail (e.g., due to markup content), the layout throws an exception and the appender discards the entire log event. This behavior enables an attacker to suppress logging of their own requests, potentially evading detection. The vulnerability affects log4net versions >=1.2.11 and <3.5.0 and only impacts applications on ASP.NET for .NET Framework using the %aspnet-request layout. The issue is fixed in version 3.5.0.
Potential Impact
An attacker can craft requests that cause ASP.NET request validation to fail, triggering exceptions in the logging layout that result in the entire log event being discarded. This allows suppression of log records for those requests, reducing visibility and potentially aiding evasion of detection or forensic analysis. There is no direct impact on confidentiality or availability, but integrity of logging is affected.
Mitigation Recommendations
Users should upgrade Apache log4net to version 3.5.0 or later, where this issue is fixed. No other mitigations are indicated. Patch status is confirmed by vendor advisory information embedded in the description.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- apache
- Date Reserved
- 2026-10-04T16:21:12.546Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6ac5544a2cdf04f656d9e12b
Added to database: 10/06/2026, 20:04:26 UTC
Last enriched: 10/06/2026, 20:19:10 UTC
Last updated: 10/06/2026, 20:19:15 UTC
Views: 9
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.