prevent Host header injection attacks

commafeed-server/src/main/java/com/commafeed/CommaFeedApplication.java

@@ -41,6 +41,11 @@ public class CommaFeedApplication {
             ImageProxyUrl.generateKey();
         }
 
+        if (config.passwordRecoveryEnabled() && config.passwordRecoveryPublicBaseUrl().isEmpty()) {
+            throw new IllegalStateException(
+                    "password recovery is enabled but no public base url is set");
+        }
+
         feedRefreshEngine.start();
         taskScheduler.start();
     }

commafeed-server/src/main/java/com/commafeed/CommaFeedConfiguration.java

@@ -49,6 +49,13 @@ public interface CommaFeedConfiguration {
     @WithDefault("false")
     boolean passwordRecoveryEnabled();
 
+    /**
+     * The base URL of the application to use in the password recovery link in the email. We can't
+     * use the URL sent by the browser of the user because of malicious Host header injection
+     * attacks.
+     */
+    Optional<String> passwordRecoveryPublicBaseUrl();
+
     /** Message displayed in a notification at the bottom of the page. */
     Optional<String> announcement();
 

commafeed-server/src/main/java/com/commafeed/frontend/resource/UserREST.java

@@ -413,7 +413,8 @@ public class UserREST {
     }
 
     private String buildEmailContent(User user) throws URISyntaxException {
-        String publicUrl = Urls.removeTrailingSlash(uri.getBaseUri().toString());
+        String publicUrl =
+                Urls.removeTrailingSlash(config.passwordRecoveryPublicBaseUrl().orElseThrow());
         return String.format(
                 "You asked for password recovery for account '%s', <a href='%s'>follow this link</a> to change your password. Ignore this if you didn't request a password recovery.",
                 user.getName(), callbackUrl(user, publicUrl));