diff --git a/bootstrap/helpers/socialite.php b/bootstrap/helpers/socialite.php
index 5f7e8d868a..f9bbecbd2e 100644
--- a/bootstrap/helpers/socialite.php
+++ b/bootstrap/helpers/socialite.php
@@ -9,12 +9,20 @@ use Laravel\Socialite\Two\GithubProvider;
 use SocialiteProviders\Discord\Provider;
 use SocialiteProviders\Manager\Config;
 
+/**
+ * Callback URL built from the instance URL, never from the request Host header.
+ */
+function oauth_default_redirect_uri(string $provider): string
+{
+    return rtrim(base_url(), '/').route('auth.callback', $provider, false);
+}
+
 function get_socialite_provider(string $provider)
 {
     $oauth_setting = OauthSetting::firstWhere('provider', $provider);
 
     if (! filled($oauth_setting->redirect_uri)) {
-        $oauth_setting->update(['redirect_uri' => route('auth.callback', $provider)]);
+        $oauth_setting->redirect_uri = oauth_default_redirect_uri($provider);
     }
 
     if ($provider === 'azure') {
diff --git a/database/migrations/2026_09_29_200325_add_created_before_oauth_identities_to_users_table.php b/database/migrations/2026_09_29_200325_add_created_before_oauth_identities_to_users_table.php
index 9828ff8e89..8d50838ce4 100644
--- a/database/migrations/2026_09_29_200325_add_created_before_oauth_identities_to_users_table.php
+++ b/database/migrations/2026_09_29_200325_add_created_before_oauth_identities_to_users_table.php
@@ -8,9 +8,12 @@ use Illuminate\Support\Facades\Schema;
 return new class extends Migration
 {
     /**
-     * Before OAuth identities existed, OAuth sign-in matched users by email only.
-     * Mark every user that exists at upgrade time so their first OAuth identity
-     * links without a provider email verification claim.
+     * Before OAuth identities existed, OAuth sign-in matched users by email only
+     * and created users without a password. Mark those password-less users so
+     * their first OAuth identity links without a provider email verification
+     * claim. Users with a password (including root) never get this exemption:
+     * otherwise anyone with an unverified provider account with their email
+     * could sign in as them.
      */
     public function up(): void
     {
@@ -18,7 +21,9 @@ return new class extends Migration
             $table->boolean('created_before_oauth_identities')->default(false);
         });
 
-        DB::table('users')->update(['created_before_oauth_identities' => true]);
+        DB::table('users')
+            ->whereNull('password')
+            ->update(['created_before_oauth_identities' => true]);
     }
 
     public function down(): void
diff --git a/resources/views/livewire/settings-oauth.blade.php b/resources/views/livewire/settings-oauth.blade.php
index 822c035b31..a24224dbcb 100644
--- a/resources/views/livewire/settings-oauth.blade.php
+++ b/resources/views/livewire/settings-oauth.blade.php
@@ -58,7 +58,7 @@
                         @if ($provider === 'oidc')
                             <x-forms.input canGate="update" :canResource="$settings"
                                 id="oauth_settings_map.{{ $provider }}.redirect_uri"
-                                placeholder="{{ route('auth.callback', $provider) }}" label="Redirect URI" />
+                                placeholder="{{ oauth_default_redirect_uri($provider) }}" label="Redirect URI" />
                             <x-forms.input canGate="update" :canResource="$settings"
                                 id="oauth_settings_map.{{ $provider }}.base_url" label="Issuer URL" required
                                 helper="OpenID Provider issuer URL, for example https://example.okta.com. Coolify uses it to discover the authorization, token, userinfo, and JWKS endpoints." />
@@ -81,7 +81,7 @@
                         @else
                             <x-forms.input canGate="update" :canResource="$settings"
                                 id="oauth_settings_map.{{ $provider }}.redirect_uri"
-                                placeholder="{{ route('auth.callback', $provider) }}" label="Redirect URI" />
+                                placeholder="{{ oauth_default_redirect_uri($provider) }}" label="Redirect URI" />
                             <x-forms.input canGate="update" :canResource="$settings"
                                 id="oauth_settings_map.{{ $provider }}.client_id" label="Client ID" required />
                             <x-forms.input canGate="update" :canResource="$settings"
diff --git a/tests/Feature/OauthControllerTest.php b/tests/Feature/OauthControllerTest.php
index 306c048be3..5568407662 100644
--- a/tests/Feature/OauthControllerTest.php
+++ b/tests/Feature/OauthControllerTest.php
@@ -257,18 +257,108 @@ it('links an existing account on the first login after upgrade from the real pro
     ]],
 ]);
 
-it('marks only users that exist at upgrade time as created before OAuth identities', function () {
-    $existingUser = User::factory()->create();
+function rerunCreatedBeforeOauthIdentitiesMigration(): void
+{
     $migration = require database_path('migrations/2026_09_29_200325_add_created_before_oauth_identities_to_users_table.php');
     $migration->down();
     $migration->up();
+}
 
-    $newUser = User::factory()->create();
+/**
+ * Brings the users into the state after an upgrade from v4.3.23.
+ */
+function upgradeUsersToOauthIdentities(): void
+{
+    rerunCreatedBeforeOauthIdentitiesMigration();
+}
 
-    expect($existingUser->refresh()->created_before_oauth_identities)->toBeTrue()
+it('marks only password-less users that exist at upgrade time as created before OAuth identities', function () {
+    $rootUser = User::factory()->create(['id' => 0]);
+    $passwordUser = User::factory()->create();
+    $oauthCreatedUser = User::factory()->create(['password' => null]);
+
+    rerunCreatedBeforeOauthIdentitiesMigration();
+
+    $newUser = User::factory()->create(['password' => null]);
+
+    expect($oauthCreatedUser->refresh()->created_before_oauth_identities)->toBeTrue()
+        ->and($rootUser->refresh()->created_before_oauth_identities)->toBeFalse()
+        ->and($passwordUser->refresh()->created_before_oauth_identities)->toBeFalse()
         ->and($newUser->refresh()->created_before_oauth_identities)->toBeFalse();
 });
 
+it('does not link an unverified provider email to a password user after the upgrade', function (string $provider, array $rawClaims) {
+    $user = User::factory()->create(['id' => 0, 'email' => 'root@example.com']);
+    $setting = OauthSetting::updateOrCreate(['provider' => $provider], [
+        'client_id' => 'client-id',
+        'client_secret' => 'client-secret',
+        'base_url' => 'https://auth.example.com',
+        'enabled' => true,
+    ]);
+    upgradeUsersToOauthIdentities();
+
+    expect(fn () => app(OauthLoginService::class)->login($provider, (object) [
+        'email' => 'root@example.com',
+        'name' => 'Attacker',
+        'id' => 'attacker-provider-id',
+        'user' => $rawClaims,
+    ], $setting))->toThrow(HttpException::class, 'OAuth provider did not verify the email address');
+
+    $this->assertGuest();
+    expect(OauthIdentity::count())->toBe(0)
+        ->and($user->refresh()->created_before_oauth_identities)->toBeFalse();
+})->with([
+    'discord unverified' => ['discord', ['verified' => false]],
+    'authentik default email scope' => ['authentik', ['email_verified' => false]],
+]);
+
+it('links a verified provider email to a password user after the upgrade', function (string $provider, array $rawClaims) {
+    $user = User::factory()->create(['email' => 'member@example.com']);
+    $setting = OauthSetting::updateOrCreate(['provider' => $provider], [
+        'client_id' => 'client-id',
+        'client_secret' => 'client-secret',
+        'enabled' => true,
+    ]);
+    upgradeUsersToOauthIdentities();
+
+    $resolvedUser = app(OauthLoginService::class)->login($provider, (object) [
+        'email' => 'member@example.com',
+        'name' => 'Member',
+        'id' => 'member-provider-id',
+        'user' => $rawClaims,
+    ], $setting);
+
+    expect($resolvedUser->is($user))->toBeTrue()
+        ->and(OauthIdentity::where(['user_id' => $user->id, 'provider' => $provider])->exists())->toBeTrue();
+    $this->assertAuthenticatedAs($user);
+})->with([
+    'github' => ['github', []],
+    'google verified' => ['google', ['email_verified' => true, 'hd' => 'example.com']],
+    'discord verified' => ['discord', ['verified' => true]],
+]);
+
+it('links a password-less user from before the upgrade without an email verification claim', function () {
+    $user = User::factory()->create(['email' => 'legacy@example.com', 'password' => null]);
+    $setting = OauthSetting::create([
+        'provider' => 'discord',
+        'client_id' => 'discord-client-id',
+        'client_secret' => 'discord-client-secret',
+        'enabled' => true,
+    ]);
+    upgradeUsersToOauthIdentities();
+
+    $resolvedUser = app(OauthLoginService::class)->login('discord', (object) [
+        'email' => 'legacy@example.com',
+        'name' => 'Legacy User',
+        'id' => 'legacy-discord-id',
+        'user' => ['verified' => false],
+    ], $setting);
+
+    expect($resolvedUser->is($user))->toBeTrue()
+        ->and($user->refresh()->created_before_oauth_identities)->toBeFalse();
+    $this->assertAuthenticatedAs($user);
+});
+
 it('links a user from before the upgrade without an email verification claim', function (string $provider, array $rawClaims, ?string $password) {
     $user = User::factory()->create([
         'email' => 'legacy@example.com',
@@ -610,3 +700,21 @@ it('rejects a Google account outside the configured Workspace even when its emai
     expect(OauthIdentity::count())->toBe(0);
     $this->assertGuest();
 });
+
+it('sends the instance callback url without saving it when a forged host starts an oauth login', function () {
+    InstanceSettings::query()->whereKey(0)->update(['fqdn' => 'https://coolify.example.com']);
+    Once::flush();
+    OauthSetting::create([
+        'provider' => 'github',
+        'client_id' => 'github-client-id',
+        'client_secret' => 'github-client-secret',
+        'enabled' => true,
+    ]);
+
+    $response = $this->get('http://attacker.example/auth/github/redirect');
+
+    $response->assertRedirect();
+    parse_str((string) parse_url($response->headers->get('Location'), PHP_URL_QUERY), $query);
+    expect($query['redirect_uri'])->toBe('https://coolify.example.com/auth/github/callback')
+        ->and(OauthSetting::where('provider', 'github')->value('redirect_uri'))->toBeNull();
+});