The DefaultOSWorkflowConfigurator class in Jira Server and Jira Data Center before version 8.18.1 allows remote attackers who can trick a system administrator to import their malicious workflow to execute arbitrary code via a Remote Code Execution (RCE) vulnerability which allowed for various problematic OSWorkflow classes to be used as part of workflows. The fix for this issue blocks usage of unsafe conditions, validators, functions and registers that are build-in into OSWorkflow library and other Jira dependencies. Atlassian-made functions or functions provided by 3rd party plugins are not affected by this fix.
To disable the protection in Jira 8.18.1 and above administrators can enable the dark feature flag: com.atlassian.jira.security.LegacyJiraTypeResolver.WARN_ONLY.enabled.
Workaround for the vulnerability is available in Jira from version 8.5.19 (for 8.5.x) and from 8.13.11 (for 8.13.x).
To enable protection in Jira 8.5.19+ and 8.13.11+ administrators can enable the dark feature flag: