Improper Neutralization of Null Byte or NUL Character Affecting log4net package, versions [,3.5.0)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-DOTNET-LOG4NET-20550521
- published7 Oct 2026
- disclosed6 Oct 2026
- creditUnknown
Introduced: 6 Oct 2026
NewCVE-2026-105239 (opens in a new tab)How to fix?
Upgrade log4net to version 3.5.0 or higher.
Overview
Affected versions of this package are vulnerable to Improper Neutralization of Null Byte or NUL Character in EventLogAppender, which passes rendered content through to ReportEventW unescaped, and that API takes a null terminated string, so a NUL ends the stored record at that point. An attacker can have the remainder of a record silently omitted from the Windows Event Log, including exception text and trailing fields, by placing a NUL in content that reaches a logged message. This affects only Windows applications using EventLogAppender, requires the attacker to control data that is logged, and WriteEntry raises nothing, so the record is simply stored short with no error surfaced.