fix: #8135

src/groups/data.js

@@ -53,6 +53,11 @@ module.exports = function (Groups) {
 		return Array.isArray(groupsData) && groupsData[0] ? groupsData[0] : null;
 	};
 
+	Groups.getGroupField = async function (groupName, field) {
+		const groupData = await Groups.getGroupFields(groupName, [field]);
+		return groupData ? groupData[field] : null;
+	};
+
 	Groups.getGroupFields = async function (groupName, fields) {
 		const groups = await Groups.getGroupsFields([groupName], fields);
 		return groups ? groups[0] : null;

src/socket.io/groups.js

@@ -375,10 +375,12 @@ async function canModifyGroup(uid, groupName) {
 	}
 	const results = await utils.promiseParallel({
 		isOwner: groups.ownership.isOwner(uid, groupName),
-		isAdminOrGlobalMod: user.isAdminOrGlobalMod(uid),
+		system: groups.getGroupField(groupName, 'system'),
+		isAdmin: user.isAdministrator(uid),
+		isGlobalMod: user.isGlobalModerator(uid),
 	});
 
-	if (!results.isOwner && !results.isAdminOrGlobalMod) {
+	if (!(results.isOwner || results.isAdmin || (results.isGlobalMod && !results.system))) {
 		throw new Error('[[error:no-privileges]]');
 	}
 }