A bug in Entra ID restricted management administrative units allowed creating immutable users that couldn't be modified or disabled, even by Global Administrators. This could enable an attacker to protect a compromised account from containment. The issue was caused by a timing vulnerability when removing users from restricted AUs and required specific steps to remediate affected accounts.
Affected Services
Entra ID
Remediation
Add affected user to a new restricted management AU, then delete that AU without first removing the user. Wait 5-10 minutes for restricted status to clear.