Quick answers
- Is CVE-2026-105242 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-105242 being exploited in the wild.
- How severe is CVE-2026-105242?
- Medium severity, with a CVSS score of 5.3, published 6 October 2026.
- Which products and versions are affected?
- Apache Log4net 1.2.11 before 3.5.0.
- Is there a fix for CVE-2026-105242?
- Yes: fixed in 3.5.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-105242 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-105242?
- Check whether you run Apache Log4net at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: 3.5.0
Technical details
The aspnet-request pattern converter in log4net reads HttpRequest.Params to extract request details; this triggers ASP.NET request validation that rejects content such as markup and throws an exception. When the exception occurs inside the layout processing, the AppenderSkeleton discards the entire log event instead of recording it. An unauthenticated attacker on the network can send a request with crafted parameters to suppress logging. The fix reads through HttpRequest.Unvalidated instead to preserve the event and adds broader exception handling for body parsing and ServerVariables access.
Affected products
- Apache log4net 1.2.11 before 3.5.0
Timeline
- 2026-10-06: disclosed
- 2026-09-04: patched