How to block access to URLs vulnerable to SECURITY-2349/CVE-2021-21648

 import com.cloudbees.jenkins.plugins.requestfilter.*

 String mitigationPattern = '.*[/\\\\]upload[/\\\\].*("|%22).*[/\\\\](upload|complete).*'
 int responseCode = 403
 String responseContent =
 '''
 <h1>Forbidden call</h1>
 For more information, please visit the <a href="https://cloudbees.com/r/block-url-pattern">following page</a>
 or <a href="https://support.cloudbees.com">contact CloudBees support</a> mentioning SECURITY-2349.
 '''
 String responseContentType = 'text/html'

 // Let's preserve existing configuration, if any.
 // Also, this code is idempotent so we can run it multiple times without worrying we'd add X times the same config
 List<Rule> existingRules = new ArrayList(Rules.get().getRules()) // reinstantiation needed bc emptyList() is immutable

 if( existingRules.collect { rule -> rule.pattern }
                  .findAll { rulePattern -> mitigationPattern.equals(rulePattern) }
                  .isEmpty() )
 {
   println "mitigation pattern not found, adding it"
   Rule mitigationRule = new Rule(mitigationPattern)
   mitigationRule.setResponse(new Response(responseCode,responseContentType,responseContent))
   existingRules.add(mitigationRule)
   Rules.get().setRules(existingRules)
 } else {
   println 'mitigation pattern found, no-op'
 }