Check access when sending TODOs related to merge requests

app/models/merge_request.rb

@@ -518,7 +518,7 @@ class MergeRequest < ApplicationRecord
       participants << merge_user
     end
 
-    participants
+    participants.select { |participant| Ability.allowed?(participant, :read_merge_request, self) }
   end
 
   def first_commit

changelogs/unreleased/security-215175-filter-merge-participants.yml

+---
+title: Check access when sending TODOs related to merge requests
+merge_request:
+author:
+type: security

spec/models/merge_request_spec.rb

@@ -3661,7 +3661,7 @@ describe MergeRequest do
 
   describe '#merge_participants' do
     it 'contains author' do
-      expect(subject.merge_participants).to eq([subject.author])
+      expect(subject.merge_participants).to contain_exactly(subject.author)
     end
 
     describe 'when merge_when_pipeline_succeeds? is true' do
@@ -3675,8 +3675,20 @@ describe MergeRequest do
                  author: user)
         end
 
-        it 'contains author only' do
-          expect(subject.merge_participants).to eq([subject.author])
+        context 'author is not a project member' do
+          it 'is empty' do
+            expect(subject.merge_participants).to be_empty
+          end
+        end
+
+        context 'author is a project member' do
+          before do
+            subject.project.team.add_reporter(user)
+          end
+
+          it 'contains author only' do
+            expect(subject.merge_participants).to contain_exactly(subject.author)
+          end
         end
       end
 
@@ -3689,8 +3701,24 @@ describe MergeRequest do
                  merge_user: merge_user)
         end
 
-        it 'contains author and merge user' do
-          expect(subject.merge_participants).to eq([subject.author, merge_user])
+        before do
+          subject.project.team.add_reporter(subject.author)
+        end
+
+        context 'merge user is not a member' do
+          it 'contains author only' do
+            expect(subject.merge_participants).to contain_exactly(subject.author)
+          end
+        end
+
+        context 'both author and merge users are project members' do
+          before do
+            subject.project.team.add_reporter(merge_user)
+          end
+
+          it 'contains author and merge user' do
+            expect(subject.merge_participants).to contain_exactly(subject.author, merge_user)
+          end
         end
       end
     end