diff --git a/src/applications/diffusion/protocol/DiffusionGitCommandEngine.php b/src/applications/diffusion/protocol/DiffusionGitCommandEngine.php
--- a/src/applications/diffusion/protocol/DiffusionGitCommandEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionGitCommandEngine.php
@@ -26,9 +26,7 @@
 
     $env['HOME'] = PhabricatorEnv::getEmptyCWD();
 
-    if ($this->isAnySSHProtocol()) {
-      $env['GIT_SSH'] = $this->getSSHWrapper();
-    }
+    $env['GIT_SSH'] = $this->getSSHWrapper();
 
     if ($this->isAnyHTTPProtocol()) {
       $uri = $this->getURI();
diff --git a/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php b/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php
--- a/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php
@@ -11,12 +11,14 @@
   protected function newFormattedCommand($pattern, array $argv) {
     $args = array();
 
-    if ($this->isAnySSHProtocol()) {
-      $pattern = "hg --config ui.ssh=%s {$pattern}";
-      $args[] = $this->getSSHWrapper();
-    } else {
-      $pattern = "hg {$pattern}";
-    }
+    // NOTE: Here, and in Git and Subversion, we override the SSH command even
+    // if the repository does not use an SSH remote, since our SSH wrapper
+    // defuses an attack against older versions of Mercurial, Git and
+    // Subversion (see T12961) and it's possible to execute this attack
+    // in indirect ways, like by using an SSH subrepo inside an HTTP repo.
+
+    $pattern = "hg --config ui.ssh=%s {$pattern}";
+    $args[] = $this->getSSHWrapper();
 
     return array($pattern, array_merge($args, $argv));
   }
diff --git a/src/applications/diffusion/protocol/DiffusionSubversionCommandEngine.php b/src/applications/diffusion/protocol/DiffusionSubversionCommandEngine.php
--- a/src/applications/diffusion/protocol/DiffusionSubversionCommandEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionSubversionCommandEngine.php
@@ -44,9 +44,7 @@
   protected function newCustomEnvironment() {
     $env = array();
 
-    if ($this->isAnySSHProtocol()) {
-      $env['SVN_SSH'] = $this->getSSHWrapper();
-    }
+    $env['SVN_SSH'] = $this->getSSHWrapper();
 
     return $env;
   }
diff --git a/src/applications/diffusion/protocol/__tests__/DiffusionCommandEngineTestCase.php b/src/applications/diffusion/protocol/__tests__/DiffusionCommandEngineTestCase.php
--- a/src/applications/diffusion/protocol/__tests__/DiffusionCommandEngineTestCase.php
+++ b/src/applications/diffusion/protocol/__tests__/DiffusionCommandEngineTestCase.php
@@ -26,7 +26,7 @@
       ));
 
     $this->assertCommandEngineFormat(
-      'hg xyz',
+      (string)csprintf('hg --config ui.ssh=%s xyz', $ssh_wrapper),
       array(
         'LANG' => 'en_US.UTF-8',
         'HGPLAIN' => '1',
@@ -102,7 +102,7 @@
       ));
 
     $this->assertCommandEngineFormat(
-      'hg xyz',
+      (string)csprintf('hg --config ui.ssh=%s xyz', $ssh_wrapper),
       array(
         'LANG' => 'en_US.UTF-8',
         'HGPLAIN' => '1',