A Cron expression form validation could enter infinite loop, potentially resulting in denial of service. The form validation for cron expressions (e.g. "Poll SCM", "Build periodically") could enter infinite loops when cron expressions only matching certain rare dates were entered, blocking request handling threads indefinitely.

References

• https://nvd.nist.gov/vuln/detail/CVE-2018-1999044
• https://jenkins.io/security/advisory/2018-08-15/#SECURITY-790
• jenkinsci/jenkins@e504691