diff --git a/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php b/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php
--- a/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php
+++ b/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php
@@ -76,7 +76,19 @@
       return $name;
     }
 
-    $same_window = $engine->getConfig('uri.same-window', false);
+    $same_window = $engine->getConfig('uri.same-window', null);
+
+    if ($same_window === null) {
+      // TODO:
+      // Instead of assuming every link as external,
+      // assume that only external links should be opened
+      // externally. This still probably creates lot of
+      // external links than needed, but less than before.
+      // https://we.phorge.it/T15161
+//    $same_window = $this->isInternalGenericURI($link);
+      $same_window = false;
+    }
+
     if ($same_window) {
       $target = null;
     } else {
diff --git a/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php b/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php
--- a/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php
+++ b/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php
@@ -116,7 +116,19 @@
 
     $engine = $this->getEngine();
 
-    $same_window = $engine->getConfig('uri.same-window', false);
+    $same_window = $engine->getConfig('uri.same-window', null);
+
+    if ($same_window === null) {
+      // TODO:
+      // Instead of assuming every link as external,
+      // assume that only external links should be opened
+      // externally. This still probably creates lot of
+      // external links than needed, but less than before.
+      // https://we.phorge.it/T15161
+//    $same_window = $this->isInternalAbsoluteURI($link);
+      $same_window = false;
+    }
+
     if ($same_window) {
       $target = null;
     } else {
diff --git a/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php b/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php
--- a/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php
+++ b/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php
@@ -130,4 +130,54 @@
     return strncmp($uri, '/', 1) == 0;
   }
 
+  /**
+   * Check if a generic URI points to an internal destination
+   *
+   * The URI can be relative or absolute
+   *
+   * @param string $uri Example '/bar/' or 'http://example.com/bar/'
+   * @return bool
+   */
+  protected function isInternalGenericURI($uri) {
+    return $this->isURIAnchor($uri)
+        || $this->isURIRelativePath($uri)
+        || $this->isInternalAbsoluteURI($uri);
+  }
+
+  /**
+   * Check if an absolute URI points to Phorge/Phabricator itself
+   *
+   * @param string $uri Example 'http://example.com/bar/'
+   * @return bool
+   */
+  protected function isInternalAbsoluteURI($uri) {
+
+    // Get the Base URI - full URI with protocol and ending with '/'
+    // It's difficult to imagine a case where this config is not defined,
+    // but better to be nice here
+    $base_uri =
+      PhabricatorEnv::getEnvConfigIfExists('phabricator.base-uri', null);
+
+    // Assume a safe default
+    if (!$base_uri) {
+      return false;
+    }
+
+    return $this->isURIStartingWith($uri, $base_uri);
+  }
+
+  /**
+   * Check whenever an URI starts with a specific prefix
+   *
+   * @param $uri string Example 'http://example.com/bar/'
+   * @param $prefix string Example 'http://example.com/'
+   * @return bool True if the first is contained in the second
+   */
+  private function isURIStartingWith($uri, $prefix) {
+    // I know that PHP 8 has 'str_starts_with()'
+    // but that is not the minimum version
+    // https://stackoverflow.com/a/2790919
+    return substr($uri, 0, strlen($prefix)) === $prefix;
+  }
+
 }