The vulnerability stems from improper synchronization in Jenkins' Reactor initialization process. The patch adds attains(COMPLETED) to two Executable tasks in Jenkins.java, indicating these anonymous inner class implementations of Executable.run() were vulnerable. These tasks handled security-critical initialization steps (cleaning obsolete items and finalizing setup) but could execute out of order due to missing synchronization constraints, leading to incomplete security configuration. The direct correlation between the patch and security advisory confirms these functions' role in the race condition.