Vulnerability in Apache Software Foundation Apache log4net

[ Description ]Official 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.

[ Fixes ]Fixes and patches

• Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD
• Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD

[ Advisories ]Government CERT advisories

• BSI CERT-Bund6 Oct 2026WID-SEC-2026-3772

  Apache log4net: Multiple vulnerabilities allow file manipulation Translated from German

  CVE-2026-105240CVE-2026-105239CVE-2026-105243+3 more CVEs

[ References ]References

• github.com/apache/logging-log4net/commit/77717061b20d4346b6c0ce6b54643d85fb348bc7Patch
• github.com/apache/logging-log4net/pull/315PatchVendor Advisory
• lists.apache.org/thread.html/q7649hhdodthoqw8jsjgtnb4m8qfy6d6Mailing ListVendor Advisory
• www.openwall.com/lists/oss-security/2026/10/07/19Mailing ListThird Party Advisory