diff --git a/lib/pleroma/web/oauth/oauth_controller.ex b/lib/pleroma/web/oauth/oauth_controller.ex
index 35a7c582e..3f8e3b074 100644
--- a/lib/pleroma/web/oauth/oauth_controller.ex
+++ b/lib/pleroma/web/oauth/oauth_controller.ex
@@ -64,26 +64,34 @@ defmodule Pleroma.Web.OAuth.OAuthController do
 
   defp handle_existing_authorization(
          %Plug.Conn{assigns: %{token: %Token{} = token}} = conn,
-         params
+         %{"redirect_uri" => @oob_token_redirect_uri}
        ) do
-    token = Repo.preload(token, :app)
+    render(conn, "oob_token_exists.html", %{token: token})
+  end
+
+  defp handle_existing_authorization(
+         %Plug.Conn{assigns: %{token: %Token{} = token}} = conn,
+         %{} = params
+       ) do
+    app = Repo.preload(token, :app).app
 
     redirect_uri =
       if is_binary(params["redirect_uri"]) do
         params["redirect_uri"]
       else
-        default_redirect_uri(token.app)
+        default_redirect_uri(app)
       end
 
-    redirect_uri = redirect_uri(conn, redirect_uri)
-
-    if redirect_uri == @oob_token_redirect_uri do
-      render(conn, "oob_token_exists.html", %{token: token})
-    else
+    if redirect_uri in String.split(app.redirect_uris) do
+      redirect_uri = redirect_uri(conn, redirect_uri)
       url_params = %{access_token: token.token}
       url_params = UriHelper.append_param_if_present(url_params, :state, params["state"])
       url = UriHelper.append_uri_params(redirect_uri, url_params)
       redirect(conn, external: url)
+    else
+      conn
+      |> put_flash(:error, "Unlisted redirect_uri.")
+      |> redirect(external: redirect_uri(conn, redirect_uri))
     end
   end
 
@@ -101,17 +109,27 @@ defmodule Pleroma.Web.OAuth.OAuthController do
   end
 
   def after_create_authorization(%Plug.Conn{} = conn, %Authorization{} = auth, %{
+        "authorization" => %{"redirect_uri" => @oob_token_redirect_uri}
+      }) do
+    render(conn, "oob_authorization_created.html", %{auth: auth})
+  end
+
+  def after_create_authorization(%Plug.Conn{} = conn, %Authorization{} = auth, %{
         "authorization" => %{"redirect_uri" => redirect_uri} = auth_attrs
       }) do
-    redirect_uri = redirect_uri(conn, redirect_uri)
+    app = Repo.preload(auth, :app).app
 
-    if redirect_uri == @oob_token_redirect_uri do
-      render(conn, "oob_authorization_created.html", %{auth: auth})
-    else
+    # An extra safety measure before we redirect (also done in `do_create_authorization/2`)
+    if redirect_uri in String.split(app.redirect_uris) do
+      redirect_uri = redirect_uri(conn, redirect_uri)
       url_params = %{code: auth.token}
       url_params = UriHelper.append_param_if_present(url_params, :state, auth_attrs["state"])
       url = UriHelper.append_uri_params(redirect_uri, url_params)
       redirect(conn, external: url)
+    else
+      conn
+      |> put_flash(:error, "Unlisted redirect_uri.")
+      |> redirect(external: redirect_uri(conn, redirect_uri))
     end
   end
 
@@ -324,7 +342,7 @@ defmodule Pleroma.Web.OAuth.OAuthController do
             })
 
           conn
-          |> put_session(:registration_id, registration.id)
+          |> put_session_registration_id(registration.id)
           |> registration_details(%{"authorization" => registration_params})
       end
     else
@@ -445,7 +463,7 @@ defmodule Pleroma.Web.OAuth.OAuthController do
     |> Scopes.validates(app.scopes)
   end
 
-  defp default_redirect_uri(%App{} = app) do
+  def default_redirect_uri(%App{} = app) do
     app.redirect_uris
     |> String.split()
     |> Enum.at(0)
diff --git a/test/web/oauth/oauth_controller_test.exs b/test/web/oauth/oauth_controller_test.exs
index 242b7fdb3..aae34804d 100644
--- a/test/web/oauth/oauth_controller_test.exs
+++ b/test/web/oauth/oauth_controller_test.exs
@@ -10,6 +10,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
   alias Pleroma.Registration
   alias Pleroma.Repo
   alias Pleroma.Web.OAuth.Authorization
+  alias Pleroma.Web.OAuth.OAuthController
   alias Pleroma.Web.OAuth.Token
 
   @oauth_config_path [:oauth2, :issue_new_refresh_token]
@@ -49,7 +50,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
           %{
             "response_type" => "code",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
             "scope" => "read"
           }
         )
@@ -72,7 +73,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "authorization" => %{
               "scope" => "read follow",
               "client_id" => app.client_id,
-              "redirect_uri" => app.redirect_uris,
+              "redirect_uri" => OAuthController.default_redirect_uri(app),
               "state" => "a_state"
             }
           }
@@ -98,11 +99,12 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
     test "with user-bound registration, GET /oauth/<provider>/callback redirects to `redirect_uri` with `code`",
          %{app: app, conn: conn} do
       registration = insert(:registration)
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       state_params = %{
         "scope" => Enum.join(app.scopes, " "),
         "client_id" => app.client_id,
-        "redirect_uri" => app.redirect_uris,
+        "redirect_uri" => redirect_uri,
         "state" => ""
       }
 
@@ -121,7 +123,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
           )
 
         assert response = html_response(conn, 302)
-        assert redirected_to(conn) =~ ~r/#{app.redirect_uris}\?code=.+/
+        assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
       end
     end
 
@@ -132,7 +134,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
       state_params = %{
         "scope" => "read write",
         "client_id" => app.client_id,
-        "redirect_uri" => app.redirect_uris,
+        "redirect_uri" => OAuthController.default_redirect_uri(app),
         "state" => "a_state"
       }
 
@@ -165,7 +167,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
       state_params = %{
         "scope" => Enum.join(app.scopes, " "),
         "client_id" => app.client_id,
-        "redirect_uri" => app.redirect_uris,
+        "redirect_uri" => OAuthController.default_redirect_uri(app),
         "state" => ""
       }
 
@@ -199,7 +201,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "authorization" => %{
               "scopes" => app.scopes,
               "client_id" => app.client_id,
-              "redirect_uri" => app.redirect_uris,
+              "redirect_uri" => OAuthController.default_redirect_uri(app),
               "state" => "a_state",
               "nickname" => nil,
               "email" => "john@doe.com"
@@ -218,6 +220,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
            conn: conn
          } do
       registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       conn =
         conn
@@ -229,7 +232,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "authorization" => %{
               "scopes" => app.scopes,
               "client_id" => app.client_id,
-              "redirect_uri" => app.redirect_uris,
+              "redirect_uri" => redirect_uri,
               "state" => "a_state",
               "nickname" => "availablenick",
               "email" => "available@email.com"
@@ -238,7 +241,36 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         )
 
       assert response = html_response(conn, 302)
-      assert redirected_to(conn) =~ ~r/#{app.redirect_uris}\?code=.+/
+      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
+    end
+
+    test "with unlisted `redirect_uri`, POST /oauth/register?op=register results in HTTP 401",
+         %{
+           app: app,
+           conn: conn
+         } do
+      registration = insert(:registration, user: nil, info: %{"nickname" => nil, "email" => nil})
+      unlisted_redirect_uri = "http://cross-site-request.com"
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post(
+          "/oauth/register",
+          %{
+            "op" => "register",
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => unlisted_redirect_uri,
+              "state" => "a_state",
+              "nickname" => "availablenick",
+              "email" => "available@email.com"
+            }
+          }
+        )
+
+      assert response = html_response(conn, 401)
     end
 
     test "with invalid params, POST /oauth/register?op=register renders registration_details page",
@@ -254,7 +286,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         "authorization" => %{
           "scopes" => app.scopes,
           "client_id" => app.client_id,
-          "redirect_uri" => app.redirect_uris,
+          "redirect_uri" => OAuthController.default_redirect_uri(app),
           "state" => "a_state",
           "nickname" => "availablenickname",
           "email" => "available@email.com"
@@ -286,6 +318,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
          } do
       user = insert(:user, password_hash: Comeonin.Pbkdf2.hashpwsalt("testpassword"))
       registration = insert(:registration, user: nil)
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       conn =
         conn
@@ -297,7 +330,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "authorization" => %{
               "scopes" => app.scopes,
               "client_id" => app.client_id,
-              "redirect_uri" => app.redirect_uris,
+              "redirect_uri" => redirect_uri,
               "state" => "a_state",
               "name" => user.nickname,
               "password" => "testpassword"
@@ -306,7 +339,37 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         )
 
       assert response = html_response(conn, 302)
-      assert redirected_to(conn) =~ ~r/#{app.redirect_uris}\?code=.+/
+      assert redirected_to(conn) =~ ~r/#{redirect_uri}\?code=.+/
+    end
+
+    test "with unlisted `redirect_uri`, POST /oauth/register?op=connect results in HTTP 401`",
+         %{
+           app: app,
+           conn: conn
+         } do
+      user = insert(:user, password_hash: Comeonin.Pbkdf2.hashpwsalt("testpassword"))
+      registration = insert(:registration, user: nil)
+      unlisted_redirect_uri = "http://cross-site-request.com"
+
+      conn =
+        conn
+        |> put_session(:registration_id, registration.id)
+        |> post(
+          "/oauth/register",
+          %{
+            "op" => "connect",
+            "authorization" => %{
+              "scopes" => app.scopes,
+              "client_id" => app.client_id,
+              "redirect_uri" => unlisted_redirect_uri,
+              "state" => "a_state",
+              "name" => user.nickname,
+              "password" => "testpassword"
+            }
+          }
+        )
+
+      assert response = html_response(conn, 401)
     end
 
     test "with invalid params, POST /oauth/register?op=connect renders registration_details page",
@@ -322,7 +385,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         "authorization" => %{
           "scopes" => app.scopes,
           "client_id" => app.client_id,
-          "redirect_uri" => app.redirect_uris,
+          "redirect_uri" => OAuthController.default_redirect_uri(app),
           "state" => "a_state",
           "name" => user.nickname,
           "password" => "wrong password"
@@ -358,7 +421,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
           %{
             "response_type" => "code",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
             "scope" => "read"
           }
         )
@@ -378,7 +441,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "authorization" => %{
               "response_type" => "code",
               "client_id" => app.client_id,
-              "redirect_uri" => app.redirect_uris,
+              "redirect_uri" => OAuthController.default_redirect_uri(app),
               "scope" => "read"
             }
           }
@@ -399,7 +462,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
           %{
             "response_type" => "code",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
             "scope" => "read",
             "force_login" => "true"
           }
@@ -423,7 +486,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
           %{
             "response_type" => "code",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => OAuthController.default_redirect_uri(app),
             "state" => "specific_client_state",
             "scope" => "read"
           }
@@ -433,6 +496,31 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
                "https://redirect.url?access_token=#{token.token}&state=specific_client_state"
     end
 
+    test "with existing authentication and unlisted non-OOB `redirect_uri`, redirects without credentials",
+         %{
+           app: app,
+           conn: conn
+         } do
+      unlisted_redirect_uri = "http://cross-site-request.com"
+      token = insert(:oauth_token, app_id: app.id)
+
+      conn =
+        conn
+        |> put_session(:oauth_token, token.token)
+        |> get(
+          "/oauth/authorize",
+          %{
+            "response_type" => "code",
+            "client_id" => app.client_id,
+            "redirect_uri" => unlisted_redirect_uri,
+            "state" => "specific_client_state",
+            "scope" => "read"
+          }
+        )
+
+      assert redirected_to(conn) == unlisted_redirect_uri
+    end
+
     test "with existing authentication and OOB `redirect_uri`, redirects to app with `token` and `state` params",
          %{
            app: app,
@@ -461,6 +549,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
     test "redirects with oauth authorization" do
       user = insert(:user)
       app = insert(:oauth_app, scopes: ["read", "write", "follow"])
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       conn =
         build_conn()
@@ -469,14 +558,14 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "name" => user.nickname,
             "password" => "test",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => redirect_uri,
             "scope" => "read write",
             "state" => "statepassed"
           }
         })
 
       target = redirected_to(conn)
-      assert target =~ app.redirect_uris
+      assert target =~ redirect_uri
 
       query = URI.parse(target).query |> URI.query_decoder() |> Map.new()
 
@@ -489,6 +578,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
     test "returns 401 for wrong credentials", %{conn: conn} do
       user = insert(:user)
       app = insert(:oauth_app)
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       result =
         conn
@@ -497,7 +587,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "name" => user.nickname,
             "password" => "wrong",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => redirect_uri,
             "state" => "statepassed",
             "scope" => Enum.join(app.scopes, " ")
           }
@@ -506,7 +596,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       # Keep the details
       assert result =~ app.client_id
-      assert result =~ app.redirect_uris
+      assert result =~ redirect_uri
 
       # Error message
       assert result =~ "Invalid Username/Password"
@@ -515,6 +605,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
     test "returns 401 for missing scopes", %{conn: conn} do
       user = insert(:user)
       app = insert(:oauth_app)
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       result =
         conn
@@ -523,7 +614,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "name" => user.nickname,
             "password" => "test",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => redirect_uri,
             "state" => "statepassed",
             "scope" => ""
           }
@@ -532,7 +623,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       # Keep the details
       assert result =~ app.client_id
-      assert result =~ app.redirect_uris
+      assert result =~ redirect_uri
 
       # Error message
       assert result =~ "This action is outside the authorized scopes"
@@ -541,6 +632,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
     test "returns 401 for scopes beyond app scopes", %{conn: conn} do
       user = insert(:user)
       app = insert(:oauth_app, scopes: ["read", "write"])
+      redirect_uri = OAuthController.default_redirect_uri(app)
 
       result =
         conn
@@ -549,7 +641,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
             "name" => user.nickname,
             "password" => "test",
             "client_id" => app.client_id,
-            "redirect_uri" => app.redirect_uris,
+            "redirect_uri" => redirect_uri,
             "state" => "statepassed",
             "scope" => "read write follow"
           }
@@ -558,7 +650,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
 
       # Keep the details
       assert result =~ app.client_id
-      assert result =~ app.redirect_uris
+      assert result =~ redirect_uri
 
       # Error message
       assert result =~ "This action is outside the authorized scopes"
@@ -577,7 +669,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         |> post("/oauth/token", %{
           "grant_type" => "authorization_code",
           "code" => auth.token,
-          "redirect_uri" => app.redirect_uris,
+          "redirect_uri" => OAuthController.default_redirect_uri(app),
           "client_id" => app.client_id,
           "client_secret" => app.client_secret
         })
@@ -631,7 +723,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         |> post("/oauth/token", %{
           "grant_type" => "authorization_code",
           "code" => auth.token,
-          "redirect_uri" => app.redirect_uris
+          "redirect_uri" => OAuthController.default_redirect_uri(app)
         })
 
       assert %{"access_token" => token, "scope" => scope} = json_response(conn, 200)
@@ -676,7 +768,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         |> post("/oauth/token", %{
           "grant_type" => "authorization_code",
           "code" => auth.token,
-          "redirect_uri" => app.redirect_uris
+          "redirect_uri" => OAuthController.default_redirect_uri(app)
         })
 
       assert resp = json_response(conn, 400)
@@ -755,7 +847,7 @@ defmodule Pleroma.Web.OAuth.OAuthControllerTest do
         |> post("/oauth/token", %{
           "grant_type" => "authorization_code",
           "code" => "Imobviouslyinvalid",
-          "redirect_uri" => app.redirect_uris,
+          "redirect_uri" => OAuthController.default_redirect_uri(app),
           "client_id" => app.client_id,
           "client_secret" => app.client_secret
         })