Vulnerability in Apache Software Foundation Apache log4net

[ Description ]Official description

Improper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net. Content that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw. Every buffered event in the batch was discarded, not only the one carrying the content, and a truncated mail could be left in the pickup directory. A party whose data reaches a log message could suppress the records of other events. Only applications that use SmtpPickupDirAppender 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.

[ 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/4d2e10f0908199604b4326f9df6d0b43b871e333Patch
• github.com/apache/logging-log4net/pull/315Patch
• lists.apache.org/thread.html/hg8dgh3oy8bp3dhb8nsygk9kw2o401wsMailing ListVendor Advisory
• www.openwall.com/lists/oss-security/2026/10/07/15Mailing ListThird Party Advisory