Cross-Site Request Forgery in Jenkins

An extension point in Jenkins allows selectively disabling cross-site request forgery (CSRF) protection for specific URLs.

Implementations of that extension point received a different representation of the URL path than the Stapler web framework uses to dispatch requests in Jenkins 2.227 and earlier, LTS 2.204.5 and earlier. This discrepancy allowed attackers to craft URLs that would bypass the CSRF protection of any target URL.

Jenkins now uses the same representation of the URL path to decide whether CSRF protection is needed for a given URL as the Stapler web framework uses.

In case of problems, administrators can disable this security fix by setting the system property hudson.security.csrf.CrumbFilter.UNPROCESSED_PATHINFO to true.

As an additional safeguard, semicolon (;) characters in the path part of a URL are now banned by default. Administrators can disable this protection by setting the system property jenkins.security.SuspiciousRequestFilter.allowSemicolonsInPath to true.