All vulnerabilities
CVE-2026-105244

Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content

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 in3.5.0Also 77717061b20d4346b6c0ce6b54643d85fb348bc7CVE List
Published6 Oct 2026Updated 7 Oct 2026CVE List

What fixes it

  • 3.5.0Apache log4netCVE List
  • 77717061b20d4346b6c0ce6b54643d85fb348bc7Apache log4netCVE List

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 Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net.

Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected.

This issue affects Apache log4net: from 1.2.12 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: 1.2.12 before 3.5.0CVE List
  • Apache log4netaffected: 56a2e146e21ff4737e1ff3ec308810e667873947 before 77717061b20d4346b6c0ce6b54643d85fb348bc7CVE List

References 3