Subgroup circular references causes infinite loop

[VeyJulien]

Bug Report

Prerequisites

• Did you reproduce the problem on TYPO3 v11.5 LTS?

Description

Hi, I work at GAYA and due to a user group misconfiguration of one of our clients we had some error 500 showing up in our logs. They made a circular reference within their groups which caused infinite loop.
We thought that it could happen to others and that we should suggest a workaround.

Steps to Reproduce

1. Create the "Group 1" user group.
2. Create the "Group 2" user group.
3. Attach the "Group 2" to the "Group 1" subgroup field.
4. Attach the "Group 1" to the "Group 2" subgroup field.
5. Attach one of this two groups to a backend user.
6. Go to /typo3/module/myusermanagement/MyUserManagementUseraccess
7. Error 500: Allowed memory size of 268435456 bytes exhausted (tried to allocate 20480 bytes) in /var/www/html/web/typo3conf/ext/my_user_management/Classes/Domain/Model/BackendUser.php on line 71

Expected behavior: Processing all groups and subgroups without looping indefinitely.

Actual behavior: Error 500.

Version

7.0.0