diff --git a/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php b/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php
index fec7c1f8af..767cfe5290 100644
--- a/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php
+++ b/src/applications/repository/worker/commitmessageparser/PhabricatorRepositoryCommitMessageParserWorker.php
@@ -1,372 +1,417 @@
 <?php
 
 abstract class PhabricatorRepositoryCommitMessageParserWorker
   extends PhabricatorRepositoryCommitParserWorker {
 
   protected function getImportStepFlag() {
     return PhabricatorRepositoryCommit::IMPORTED_MESSAGE;
   }
 
   abstract protected function getFollowupTaskClass();
 
   final protected function parseCommit(
     PhabricatorRepository $repository,
     PhabricatorRepositoryCommit $commit) {
 
     if (!$this->shouldSkipImportStep()) {
       $viewer = PhabricatorUser::getOmnipotentUser();
 
       $refs_raw = DiffusionQuery::callConduitWithDiffusionRequest(
         $viewer,
         DiffusionRequest::newFromDictionary(
           array(
             'repository' => $repository,
             'user' => $viewer,
           )),
         'diffusion.querycommits',
         array(
           'repositoryPHID' => $repository->getPHID(),
           'phids' => array($commit->getPHID()),
           'bypassCache' => true,
           'needMessages' => true,
         ));
 
       if (empty($refs_raw['data'])) {
         throw new Exception(
           pht(
             'Unable to retrieve details for commit "%s"!',
             $commit->getPHID()));
       }
 
       $ref = DiffusionCommitRef::newFromConduitResult(head($refs_raw['data']));
       $this->updateCommitData($ref);
     }
 
     if ($this->shouldQueueFollowupTasks()) {
       $this->queueTask(
         $this->getFollowupTaskClass(),
         array(
           'commitID' => $commit->getID(),
         ),
         array(
           // We queue followup tasks at default priority so that the queue
           // finishes work it has started before starting more work. If
           // followups are queued at the same priority level, we do all
           // message parses first, then all change parses, etc. This makes
           // progress uneven. See T11677 for discussion.
           'priority' => PhabricatorWorker::PRIORITY_DEFAULT,
         ));
     }
   }
 
   final protected function updateCommitData(DiffusionCommitRef $ref) {
     $commit = $this->commit;
     $author = $ref->getAuthor();
     $message = $ref->getMessage();
     $committer = $ref->getCommitter();
     $hashes = $ref->getHashes();
 
     $data = id(new PhabricatorRepositoryCommitData())->loadOneWhere(
       'commitID = %d',
       $commit->getID());
     if (!$data) {
       $data = new PhabricatorRepositoryCommitData();
     }
     $data->setCommitID($commit->getID());
     $data->setAuthorName(id(new PhutilUTF8StringTruncator())
       ->setMaximumBytes(255)
       ->truncateString((string)$author));
 
     $data->setCommitDetail('authorEpoch', $ref->getAuthorEpoch());
     $data->setCommitDetail('authorName', $ref->getAuthorName());
     $data->setCommitDetail('authorEmail', $ref->getAuthorEmail());
 
     $data->setCommitDetail(
       'authorPHID',
       $this->resolveUserPHID($commit, $author));
 
     $data->setCommitMessage($message);
 
     if (strlen($committer)) {
       $data->setCommitDetail('committer', $committer);
 
       $data->setCommitDetail('committerName', $ref->getCommitterName());
       $data->setCommitDetail('committerEmail', $ref->getCommitterEmail());
 
       $data->setCommitDetail(
         'committerPHID',
         $this->resolveUserPHID($commit, $committer));
     }
 
     $repository = $this->repository;
 
     $author_phid = $data->getCommitDetail('authorPHID');
     $committer_phid = $data->getCommitDetail('committerPHID');
 
     $user = new PhabricatorUser();
     if ($author_phid) {
       $user = $user->loadOneWhere(
         'phid = %s',
         $author_phid);
     }
 
     $differential_app = 'PhabricatorDifferentialApplication';
     $revision_id = null;
     $low_level_query = null;
     if (PhabricatorApplication::isClassInstalled($differential_app)) {
       $low_level_query = id(new DiffusionLowLevelCommitFieldsQuery())
         ->setRepository($repository)
         ->withCommitRef($ref);
       $field_values = $low_level_query->execute();
       $revision_id = idx($field_values, 'revisionID');
 
       if (!empty($field_values['reviewedByPHIDs'])) {
         $data->setCommitDetail(
           'reviewerPHID',
           reset($field_values['reviewedByPHIDs']));
       }
 
       $data->setCommitDetail('differential.revisionID', $revision_id);
     }
 
     if ($author_phid != $commit->getAuthorPHID()) {
       $commit->setAuthorPHID($author_phid);
     }
 
     $commit->setSummary($data->getSummary());
     $commit->save();
 
     // Figure out if we're going to try to "autoclose" related objects (e.g.,
     // close linked tasks and related revisions) and, if not, record why we
     // aren't. Autoclose can be disabled for various reasons at the repository
     // or commit levels.
 
     $force_autoclose = idx($this->getTaskData(), 'forceAutoclose', false);
     if ($force_autoclose) {
       $autoclose_reason = PhabricatorRepository::BECAUSE_AUTOCLOSE_FORCED;
     } else {
       $autoclose_reason = $repository->shouldSkipAutocloseCommit($commit);
     }
     $data->setCommitDetail('autocloseReason', $autoclose_reason);
     $should_autoclose = $force_autoclose ||
                         $repository->shouldAutocloseCommit($commit);
 
 
     // When updating related objects, we'll act under an omnipotent user to
     // ensure we can see them, but take actions as either the committer or
     // author (if we recognize their accounts) or the Diffusion application
     // (if we do not).
 
     $actor = PhabricatorUser::getOmnipotentUser();
     $acting_as_phid = nonempty(
       $committer_phid,
       $author_phid,
       id(new PhabricatorDiffusionApplication())->getPHID());
 
+    $acting_user = $this->loadActingUser($actor, $acting_as_phid);
+
     $conn_w = id(new DifferentialRevision())->establishConnection('w');
 
     // NOTE: The `differential_commit` table has a unique ID on `commitPHID`,
     // preventing more than one revision from being associated with a commit.
     // Generally this is good and desirable, but with the advent of hash
     // tracking we may end up in a situation where we match several different
     // revisions. We just kind of ignore this and pick one, we might want to
     // revisit this and do something differently. (If we match several revisions
     // someone probably did something very silly, though.)
 
     $revision = null;
     if ($revision_id) {
       $revision_query = id(new DifferentialRevisionQuery())
         ->withIDs(array($revision_id))
         ->setViewer($actor)
         ->needReviewers(true)
         ->needActiveDiffs(true);
 
       $revision = $revision_query->executeOne();
 
       if ($revision) {
         if (!$data->getCommitDetail('precommitRevisionStatus')) {
           $data->setCommitDetail(
             'precommitRevisionStatus',
             $revision->getStatus());
         }
         $commit_drev = DiffusionCommitHasRevisionEdgeType::EDGECONST;
         id(new PhabricatorEdgeEditor())
           ->addEdge($commit->getPHID(), $commit_drev, $revision->getPHID())
           ->save();
 
         queryfx(
           $conn_w,
           'INSERT IGNORE INTO %T (revisionID, commitPHID) VALUES (%d, %s)',
           DifferentialRevision::TABLE_COMMIT,
           $revision->getID(),
           $commit->getPHID());
 
         $status_closed = ArcanistDifferentialRevisionStatus::CLOSED;
         $should_close = ($revision->getStatus() != $status_closed) &&
                         $should_autoclose;
 
         if ($should_close) {
            $commit_close_xaction = id(new DifferentialTransaction())
             ->setTransactionType(DifferentialTransaction::TYPE_ACTION)
             ->setNewValue(DifferentialAction::ACTION_CLOSE)
             ->setMetadataValue('isCommitClose', true);
 
           $commit_close_xaction->setMetadataValue(
             'commitPHID',
             $commit->getPHID());
           $commit_close_xaction->setMetadataValue(
             'committerPHID',
             $committer_phid);
           $commit_close_xaction->setMetadataValue(
             'committerName',
             $data->getCommitDetail('committer'));
           $commit_close_xaction->setMetadataValue(
             'authorPHID',
             $author_phid);
           $commit_close_xaction->setMetadataValue(
             'authorName',
             $data->getAuthorName());
 
           if ($low_level_query) {
             $commit_close_xaction->setMetadataValue(
               'revisionMatchData',
               $low_level_query->getRevisionMatchData());
             $data->setCommitDetail(
               'revisionMatchData',
               $low_level_query->getRevisionMatchData());
           }
 
           $extraction_engine = id(new DifferentialDiffExtractionEngine())
             ->setViewer($actor)
             ->setAuthorPHID($acting_as_phid);
 
           $content_source = $this->newContentSource();
 
           $update_data = $extraction_engine->updateRevisionWithCommit(
             $revision,
             $commit,
             array(
               $commit_close_xaction,
             ),
             $content_source);
 
           foreach ($update_data as $key => $value) {
             $data->setCommitDetail($key, $value);
           }
         }
       }
     }
 
     if ($should_autoclose) {
       $this->closeTasks(
         $actor,
         $acting_as_phid,
         $repository,
         $commit,
-        $message);
+        $message,
+        $acting_user);
     }
 
     $data->save();
 
     $commit->writeImportStatusFlag(
       PhabricatorRepositoryCommit::IMPORTED_MESSAGE);
   }
 
   private function resolveUserPHID(
     PhabricatorRepositoryCommit $commit,
     $user_name) {
 
     return id(new DiffusionResolveUserQuery())
       ->withCommit($commit)
       ->withName($user_name)
       ->execute();
   }
 
   private function closeTasks(
     PhabricatorUser $actor,
     $acting_as,
     PhabricatorRepository $repository,
     PhabricatorRepositoryCommit $commit,
-    $message) {
+    $message,
+    PhabricatorUser $acting_user = null) {
+
+    // If we we were able to identify an author for the commit, we try to act
+    // as that user when loading tasks marked with "Fixes Txxx". This prevents
+    // mistakes where a user accidentally writes the wrong task IDs and affects
+    // tasks they can't see (and thus can't undo the status changes for).
+
+    // This is just a guard rail, not a security measure. An attacker can still
+    // forge another user's identity trivially by forging author or committer
+    // emails. We also let commits with unrecognized authors act on any task to
+    // make behavior less confusing for new installs.
+
+    if (!$acting_user) {
+      $acting_user = $actor;
+    }
 
     $maniphest = 'PhabricatorManiphestApplication';
     if (!PhabricatorApplication::isClassInstalled($maniphest)) {
       return;
     }
 
     $prefixes = ManiphestTaskStatus::getStatusPrefixMap();
     $suffixes = ManiphestTaskStatus::getStatusSuffixMap();
 
     $matches = id(new ManiphestCustomFieldStatusParser())
       ->parseCorpus($message);
 
     $task_statuses = array();
     foreach ($matches as $match) {
       $prefix = phutil_utf8_strtolower($match['prefix']);
       $suffix = phutil_utf8_strtolower($match['suffix']);
 
       $status = idx($suffixes, $suffix);
       if (!$status) {
         $status = idx($prefixes, $prefix);
       }
 
       foreach ($match['monograms'] as $task_monogram) {
         $task_id = (int)trim($task_monogram, 'tT');
         $task_statuses[$task_id] = $status;
       }
     }
 
     if (!$task_statuses) {
       return;
     }
 
     $tasks = id(new ManiphestTaskQuery())
-      ->setViewer($actor)
+      ->setViewer($acting_user)
       ->withIDs(array_keys($task_statuses))
       ->needProjectPHIDs(true)
+      ->requireCapabilities(
+        array(
+          PhabricatorPolicyCapability::CAN_VIEW,
+          PhabricatorPolicyCapability::CAN_EDIT,
+        ))
       ->execute();
 
     foreach ($tasks as $task_id => $task) {
       $xactions = array();
 
       $edge_type = ManiphestTaskHasCommitEdgeType::EDGECONST;
       $edge_xaction = id(new ManiphestTransaction())
         ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
         ->setMetadataValue('edge:type', $edge_type)
         ->setNewValue(
           array(
             '+' => array(
               $commit->getPHID() => $commit->getPHID(),
             ),
           ));
 
       $status = $task_statuses[$task_id];
       if ($status) {
         if ($task->getStatus() != $status) {
           $xactions[] = id(new ManiphestTransaction())
             ->setTransactionType(ManiphestTransaction::TYPE_STATUS)
             ->setMetadataValue('commitPHID', $commit->getPHID())
             ->setNewValue($status);
 
           $edge_xaction->setMetadataValue('commitPHID', $commit->getPHID());
         }
       }
 
       $xactions[] = $edge_xaction;
 
       $content_source = $this->newContentSource();
 
       $editor = id(new ManiphestTransactionEditor())
         ->setActor($actor)
         ->setActingAsPHID($acting_as)
         ->setContinueOnNoEffect(true)
         ->setContinueOnMissingFields(true)
         ->setUnmentionablePHIDMap(
           array($commit->getPHID() => $commit->getPHID()))
         ->setContentSource($content_source);
 
       $editor->applyTransactions($task, $xactions);
     }
   }
 
+  private function loadActingUser(PhabricatorUser $viewer, $user_phid) {
+    if (!$user_phid) {
+      return null;
+    }
+
+    $user_type = PhabricatorPeopleUserPHIDType::TYPECONST;
+    if (phid_get_type($user_phid) != $user_type) {
+      return null;
+    }
+
+    $user = id(new PhabricatorPeopleQuery())
+      ->setViewer($viewer)
+      ->withPHIDs(array($user_phid))
+      ->executeOne();
+    if (!$user) {
+      return null;
+    }
+
+    return $user;
+  }
+
+
 }