diff --git a/src/Http/Controllers/ForgotPasswordController.php b/src/Http/Controllers/ForgotPasswordController.php
index 405ed1b18b5..5563a51de96 100644
--- a/src/Http/Controllers/ForgotPasswordController.php
+++ b/src/Http/Controllers/ForgotPasswordController.php
@@ -10,7 +10,6 @@
 use Statamic\Facades\Site;
 use Statamic\Facades\URL;
 use Statamic\Http\Middleware\RedirectIfAuthenticated;
-use Statamic\Support\Str;
 
 class ForgotPasswordController extends Controller
 {
@@ -35,10 +34,18 @@ public function sendResetLinkEmail(Request $request)
         if ($url = $request->_reset_url) {
             $url = URL::makeAbsolute($url);
 
-            $isExternal = Site::all()
-                ->map(fn ($site) => $site->absoluteUrl())
-                ->filter(fn ($siteUrl) => Str::startsWith($url, $siteUrl))
-                ->isEmpty();
+            $urlDomain = parse_url($url, PHP_URL_HOST);
+            $currentRequestDomain = parse_url(url()->to('/'), PHP_URL_HOST);
+
+            $isExternal = $urlDomain
+                ? Site::all()
+                    ->map(fn ($site) => parse_url($site->absoluteUrl(), PHP_URL_HOST))
+                    ->push($currentRequestDomain)
+                    ->filter(fn ($siteDomain) => ! is_null($siteDomain))
+                    ->unique()
+                    ->filter(fn ($siteDomain) => $siteDomain === $urlDomain)
+                    ->isEmpty()
+                : false;
 
             throw_if($isExternal, ValidationException::withMessages([
                 '_reset_url' => trans('validation.url', ['attribute' => '_reset_url']),
diff --git a/tests/Auth/ForgotPasswordTest.php b/tests/Auth/ForgotPasswordTest.php
new file mode 100644
index 00000000000..6c53af2e6d3
--- /dev/null
+++ b/tests/Auth/ForgotPasswordTest.php
@@ -0,0 +1,148 @@
+<?php
+
+namespace Tests\Auth;
+
+use Illuminate\Support\Facades\Password;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Facades\User;
+use Tests\PreventSavingStacheItemsToDisk;
+use Tests\TestCase;
+
+class ForgotPasswordTest extends TestCase
+{
+    use PreventSavingStacheItemsToDisk;
+
+    protected function resolveApplicationConfiguration($app)
+    {
+        parent::resolveApplicationConfiguration($app);
+
+        $app['config']->set('app.url', 'http://absolute-url-resolved-from-request.com');
+    }
+
+    #[Test]
+    #[DataProvider('externalProvider')]
+    public function it_validates_reset_url_when_sending_reset_link_email($url, $isExternal)
+    {
+        $this->setSites([
+            'a' => ['name' => 'A', 'locale' => 'en_US', 'url' => 'http://this-site.com/'],
+            'b' => ['name' => 'B', 'locale' => 'en_US', 'url' => 'http://subdomain.this-site.com/'],
+            'c' => ['name' => 'C', 'locale' => 'fr_FR', 'url' => '/fr/'],
+        ]);
+
+        $this->simulateSuccessfulPasswordResetEmail();
+
+        User::make()
+            ->email('san@holo.com')
+            ->password('chewy')
+            ->save();
+
+        $response = $this->post('/!/auth/password/email', [
+            'email' => 'san@holo.com',
+            '_reset_url' => $url,
+        ]);
+
+        if ($isExternal) {
+            $response->assertSessionHasErrors(['_reset_url']);
+
+            return;
+        }
+
+        $response->assertSessionHasNoErrors();
+    }
+
+    public static function externalProvider()
+    {
+        return [
+            ['http://this-site.com', false],
+            ['http://this-site.com?foo', false],
+            ['http://this-site.com#anchor', false],
+            ['http://this-site.com/', false],
+            ['http://this-site.com/?foo', false],
+            ['http://this-site.com/#anchor', false],
+
+            ['http://that-site.com', true],
+            ['http://that-site.com/', true],
+            ['http://that-site.com/?foo', true],
+            ['http://that-site.com/#anchor', true],
+            ['http://that-site.com/some-slug', true],
+            ['http://that-site.com/some-slug?foo', true],
+            ['http://that-site.com/some-slug#anchor', true],
+
+            ['http://subdomain.this-site.com', false],
+            ['http://subdomain.this-site.com/', false],
+            ['http://subdomain.this-site.com/?foo', false],
+            ['http://subdomain.this-site.com/#anchor', false],
+            ['http://subdomain.this-site.com/some-slug', false],
+            ['http://subdomain.this-site.com/some-slug?foo', false],
+            ['http://subdomain.this-site.com/some-slug#anchor', false],
+
+            ['http://absolute-url-resolved-from-request.com', false],
+            ['http://absolute-url-resolved-from-request.com/', false],
+            ['http://absolute-url-resolved-from-request.com/?foo', false],
+            ['http://absolute-url-resolved-from-request.com/?anchor', false],
+            ['http://absolute-url-resolved-from-request.com/some-slug', false],
+            ['http://absolute-url-resolved-from-request.com/some-slug?foo', false],
+            ['http://absolute-url-resolved-from-request.com/some-slug#anchor', false],
+            ['/', false],
+            ['/?foo', false],
+            ['/#anchor', false],
+            ['/some-slug', false],
+            ['?foo', false],
+            ['#anchor', false],
+            ['', false],
+            [null, false],
+
+            // External domain that starts with a valid domain.
+            ['http://this-site.com.au', true],
+            ['http://this-site.com.au/', true],
+            ['http://this-site.com.au/?foo', true],
+            ['http://this-site.com.au/#anchor', true],
+            ['http://this-site.com.au/some-slug', true],
+            ['http://this-site.com.au/some-slug?foo', true],
+            ['http://this-site.com.au/some-slug#anchor', true],
+            ['http://subdomain.this-site.com.au', true],
+            ['http://subdomain.this-site.com.au/', true],
+            ['http://subdomain.this-site.com.au/?foo', true],
+            ['http://subdomain.this-site.com.au/#anchor', true],
+            ['http://subdomain.this-site.com.au/some-slug', true],
+            ['http://subdomain.this-site.com.au/some-slug?foo', true],
+            ['http://subdomain.this-site.com.au/some-slug#anchor', true],
+        ];
+    }
+
+    #[Test]
+    public function it_allows_reset_url_for_current_request_domain_when_not_in_sites_config()
+    {
+        $this->setSites([
+            'a' => ['name' => 'A', 'locale' => 'en_US', 'url' => 'http://this-site.com/'],
+        ]);
+
+        $this->simulateSuccessfulPasswordResetEmail();
+
+        User::make()
+            ->email('san@holo.com')
+            ->password('chewy')
+            ->save();
+
+        $this
+            ->post('/!/auth/password/email', [
+                'email' => 'san@holo.com',
+                '_reset_url' => 'http://absolute-url-resolved-from-request.com/some-slug',
+            ])
+            ->assertSessionHasNoErrors();
+    }
+
+    protected function simulateSuccessfulPasswordResetEmail()
+    {
+        $success = new class
+        {
+            public function sendResetLink()
+            {
+                return Password::RESET_LINK_SENT;
+            }
+        };
+
+        Password::shouldReceive('broker')->andReturn($success);
+    }
+}