[Bug]: Sub-admin gets `Insufficient permissions to change groups` error when removing a user from a group by `PATCH`

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

A sub-admin of the two groups receives the following error when attempting to remove a user (who is member of the same two groups) from a group they administer by doing PATCH req same as web browser does:

Error:

groups: Insufficient permissions to change groups

Request:

curl -u naruto:naruto \
  -H "OCS-APIRequest: true" \
  -H "Content-Type: application/json" \
  -X PATCH \
  https://nextcloud.local/ocs/v2.php/cloud/users/hinata \
  -d '{"groups":["naruto"]}'  

Response:

{
    "ocs": {
        "meta": {
            "status": "failure",
            "statuscode": 422,
            "message": ""
        },
        "data": {
            "errors": {
                "groups": "Insufficient permissions to change groups"
            }
        }
    }
}

[!NOTE]
DELETE request works

Request:

curl -u naruto:naruto \
-H "OCS-APIRequest: true" \
 -X DELETE \ 
 https://nextcloud.local/ocs/v2.php/cloud/users/sakura/groups\?groupid\=naruto

Response:

<?xml version="1.0"?>
<ocs>
<meta>
<status>ok</status>
<statuscode>200</statuscode>
<message>OK</message>
</meta>
<data/>
</ocs>

Steps to reproduce

1. Log in as admin.
2. Create two groups (e.g. naruto and boruto).
3. Create a user (e.g. naruto) and add the user (naruto) as both member and admin of the two groups.
4. Log in as the created user (naruto).
5. Create another user (e.g. hinata) and add them as a member of both groups.
6. Attempt to remove hinata from either group.

Expected behavior

The group admin should be able to remove the user from the group.

Nextcloud Server version

34

Operating system

Debian/Ubuntu

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

No response

Start by tracing the OCS users PATCH endpoint for group changes and compare its permission handling with the DELETE group-membership endpoint shown in the report. Reproduce the two-group sub-admin scenario and verify that PATCH removal succeeds without the insufficient-permissions error.