Jenkins 2.73.1 and earlier, 2.83 and earlier bundled a version of the commons-httpclient library with the vulnerability CVE-2012-6153 that incorrectly verified SSL certificates, making it susceptible to man-in-the-middle attacks. This library is widely used as a transitive dependency in Jenkins plugins. The fix for CVE-2012-6153 was backported to the version of commons-httpclient that is bundled in core and made available to plugins.