CVE-2026-40021

Range taken from the CVE record, check it before committing. make newentry in security/vuxml creates the vid.

  <vuln vid="FIXME (make newentry)">
    <topic>FIXME -- FIXME</topic>
    <affects>
      <package>
	<name>log4net</name>
	<range><lt>3.3.0</lt></range>
      </package>
    </affects>
    <description>
      <body xmlns="http://www.w3.org/1999/xhtml">
	<p>Apache Log4net's  XmlLayout
	https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list
	 and  XmlLayoutSchemaLog4J
	https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list
	, in versions before 3.3.0, fail to sanitize characters forbidden by
	the  XML 1.0 specification https://www.w3.org/TR/xml/#charsets  in MDC
	property keys and values, as well as the identity field that may carry
	attacker-influenced data. This causes an exception during
	serialization and the silent loss of the affected log event.

An
	attacker who can influence any of these fields can exploit this to
	suppress individual log records, impairing audit trails and detection
	of malicious activity.

Users are advised to upgrade to Apache Log4net
	3.3.0, which fixes this issue.</p>
      </body>
    </description>
    <references>
      <cvename>CVE-2026-40021</cvename>
      <url>https://nvd.nist.gov/vuln/detail/CVE-2026-40021</url>
    </references>
    <dates>
      <discovery>2026-04-10</discovery>
      <entry>2026-10-25</entry>
    </dates>
  </vuln>