Add hostname option to mitigate DNS rebinding

This adds the `hostname` opt to allow the server to validate the `Host` header of incoming requests to prevent DNS rebinding attacks. Needed for https://github.com/brave/browser-laptop/issues/12616.

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/server.js b/lib/server.js
index be45ddc..d0f5716 100644
--- a/lib/server.js
+++ b/lib/server.js
@@ -51,6 +51,15 @@ function Server (torrent, opts) {
     // deny them
     if (req.headers.origin == null) return false
 
+    // If a 'hostname' string is specified, deny requests with a 'Host'
+    // header that does not match the origin of the torrent server to prevent
+    // DNS rebinding attacks.
+    if (opts.hostname) {
+      if (req.headers.host !== `${opts.hostname}:${server.address().port}`) {
+        return false
+      }
+    }
+
     // The user allowed all origins
     if (opts.origin === '*') return true