Index: src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterCowsay.php
===================================================================
--- src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterCowsay.php
+++ src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterCowsay.php
@@ -29,6 +29,7 @@
       $tongue,
       $cow);
 
+    $future->setTimeout(15);
     $future->write($content);
 
     list($err, $stdout, $stderr) = $future->resolve();
Index: src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterFiglet.php
===================================================================
--- src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterFiglet.php
+++ src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterFiglet.php
@@ -14,6 +14,7 @@
     }
 
     $future = id(new ExecFuture('figlet'))
+      ->setTimeout(15)
       ->write(trim($content, "\n"));
 
     list($err, $stdout, $stderr) = $future->resolve();
Index: src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterGraphviz.php
===================================================================
--- src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterGraphviz.php
+++ src/infrastructure/markup/interpreter/PhabricatorRemarkupBlockInterpreterGraphviz.php
@@ -14,6 +14,7 @@
     }
 
     $future = id(new ExecFuture('dot -T%s', 'png'))
+      ->setTimeout(15)
       ->write(trim($content));
 
     list($err, $stdout, $stderr) = $future->resolve();
@@ -21,7 +22,9 @@
     if ($err) {
       return $this->markupError(
         pht(
-          'Execution of `dot` failed, check your syntax: %s', $stderr));
+          'Execution of `dot` failed (#%d), check your syntax: %s',
+          $err,
+          $stderr));
     }
 
     $file = PhabricatorFile::buildFromFileDataOrHash(