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CVE-2026-105239

Apache log4net: NUL character truncates EventLogAppender records

Apache Software Foundation Apache log4net
Open in ThreatlineRecord JSON
CVSS
5.3Medium
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.82%Chance of exploitation activity in the next 30 days, higher than 56% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in3.5.0Fixed versionCVE List
Published6 Oct 2026Updated 7 Oct 2026CVE List

What fixes it

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net.

A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use EventLogAppender are affected.

This issue affects Apache log4net: from 1.2.9 before 3.5.0.

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

Text from CVE List

Affected versions 2

  • Apache log4netaffected: 1.2.9 before 3.5.0CVE List
  • Apache log4netaffected: 02e1e115435888485f2e28b414d267e39e799e07 before dc5855a0720c91590fd7a81d729ea01fdd69e000CVE List

References 3