Affected versions of Atlassian Jira Server and Data Center allow attackers with access to an administrator account that has had its access revoked to modify projects' Users & Roles settings, via a Broken Authentication vulnerability in the /plugins/servlet/project-config/PROJECT/roles endpoint. The affected versions are before version 8.19.1.
CWE-287 - Improper Authentication
Improper (or broken) authentication attacks are widespread, and have accounted for many of the worst data breaches in recent years. Improper authentication attacks are a class of vulnerabilities where an attacker impersonates a legitimate user by exploiting weaknesses in either session management or credential management to gain access to the user’s account. This can result in disclosure of sensitive information, and can lead to system compromise, theft, identity theft, and fraud.