An improper certificate validation vulnerability exists in Jenkins Active Directory Plugin 2.10 and earlier in src/main/java/hudson/plugins/active_directory/ActiveDirectoryDomain.java, src/main/java/hudson/plugins/active_directory/ActiveDirectorySecurityRealm.java, src/main/java/hudson/plugins/active_directory/ActiveDirectoryUnixAuthenticationProvider.java that allows attackers to impersonate the Active Directory server Jenkins connects to for authentication if Jenkins is configured to use StartTLS.