diff --git a/cleantalk.php b/cleantalk.php
index 8ae8e2685..0e5b58dc8 100644
--- a/cleantalk.php
+++ b/cleantalk.php
@@ -2633,7 +2633,7 @@ function apbct_cookie()
     // Cookie names to validate
     $cookie_test_value = array(
         'cookies_names' => array(),
-        'check_value'   => $apbct->api_key,
+        'check_value'   => $apbct->api_key . $apbct->data['salt'],
     );
 
     // We need to skip the domain attribute for prevent including the dot to the cookie's domain on the client.
@@ -2728,11 +2728,11 @@ function apbct_cookies_test()
             return 0;
         }
 
-        $check_string = $apbct->api_key;
+        $check_string = $apbct->api_key . $apbct->data['salt'];
         // generate value
         $cookie_names = TT::getArrayValueAsArray($cookie_test, 'cookies_names');
         foreach ( $cookie_names as $cookie_name ) {
-            $check_string .= Cookie::get($cookie_name);
+            $check_string .= TT::toString(Cookie::get($cookie_name));
         }
         // check generated value with current cookie
         $check_value = TT::getArrayValueAsString($cookie_test, 'check_value');
diff --git a/tests/RootFile/TestCheckValueSalt.php b/tests/RootFile/TestCheckValueSalt.php
new file mode 100644
index 000000000..e64d1be33
--- /dev/null
+++ b/tests/RootFile/TestCheckValueSalt.php
@@ -0,0 +1,148 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Tests for the check_value salt fix in apbct_cookie() and apbct_cookies_test().
+ *
+ * Verifies that:
+ * 1. check_value includes salt, so md5(api_key) alone cannot be extracted from cookies.
+ * 2. apbct_cookies_test() validates cookies using salt.
+ * 3. Cookies without salt are rejected.
+ */
+class TestCheckValueSalt extends TestCase
+{
+    private $apbctBackup;
+    private $cookieBackup;
+
+    protected function setUp(): void
+    {
+        global $apbct;
+
+        $this->apbctBackup = $apbct;
+        $this->cookieBackup = $_COOKIE;
+
+        $apbct = (object) [
+            'api_key' => 'testkey123',
+            'data' => [
+                'salt' => 'test_salt_value',
+                'cookies_type' => 'native',
+                'key_is_ok' => 1,
+            ],
+        ];
+
+        \Cleantalk\ApbctWP\Variables\Cookie::$force_alt_cookies_global = false;
+    }
+
+    protected function tearDown(): void
+    {
+        global $apbct;
+        $apbct = $this->apbctBackup;
+        $_COOKIE = $this->cookieBackup;
+    }
+
+    /**
+     * Test that check_value with salt differs from check_value without salt.
+     * This verifies the vulnerability fix: check_value must NOT equal md5(api_key).
+     */
+    public function testCheckValueWithSaltDiffersFromWithout()
+    {
+        global $apbct;
+
+        $with_salt = md5($apbct->api_key . $apbct->data['salt']);
+        $without_salt = md5($apbct->api_key);
+
+        $this->assertNotEquals(
+            $without_salt,
+            $with_salt,
+            'check_value must not equal md5(api_key) alone - salt must change the hash'
+        );
+    }
+
+    /**
+     * Test that apbct_cookies_test() validates a cookie computed WITH salt.
+     */
+    public function testApbctCookiesTestValidatesWithSalt()
+    {
+        global $apbct;
+
+        $cookie_test_value = array(
+            'cookies_names' => array(),
+            'check_value'   => md5($apbct->api_key . $apbct->data['salt']),
+        );
+
+        $cookie_prefix = function_exists('apbct__get_cookie_prefix') ? apbct__get_cookie_prefix() : '';
+        $_COOKIE[$cookie_prefix . 'apbct_cookies_test'] = urlencode(json_encode($cookie_test_value));
+
+        $result = apbct_cookies_test();
+
+        $this->assertSame(1, $result, 'Cookie with md5(api_key + salt) must pass validation');
+    }
+
+    /**
+     * Test that apbct_cookies_test() rejects a cookie computed WITHOUT salt.
+     * This is the core of the vulnerability fix verification.
+     */
+    public function testApbctCookiesTestRejectsCookieWithoutSalt()
+    {
+        global $apbct;
+
+        $cookie_test_value = array(
+            'cookies_names' => array(),
+            'check_value'   => md5($apbct->api_key), // No salt - old vulnerable value
+        );
+
+        $cookie_prefix = function_exists('apbct__get_cookie_prefix') ? apbct__get_cookie_prefix() : '';
+        $_COOKIE[$cookie_prefix . 'apbct_cookies_test'] = urlencode(json_encode($cookie_test_value));
+
+        $result = apbct_cookies_test();
+
+        $this->assertSame(0, $result, 'Cookie with md5(api_key) without salt must be rejected');
+    }
+
+    /**
+     * Test that check_value with salt + timestamp is correctly validated.
+     */
+    public function testApbctCookiesTestValidatesWithSaltAndTimestamp()
+    {
+        global $apbct;
+
+        $timestamp = '1718000000';
+
+        $cookie_test_value = array(
+            'cookies_names' => array('ct_ps_timestamp'),
+            'check_value'   => md5($apbct->api_key . $apbct->data['salt'] . $timestamp),
+        );
+
+        $cookie_prefix = function_exists('apbct__get_cookie_prefix') ? apbct__get_cookie_prefix() : '';
+        $_COOKIE[$cookie_prefix . 'apbct_cookies_test'] = urlencode(json_encode($cookie_test_value));
+        $_COOKIE[$cookie_prefix . 'ct_ps_timestamp'] = $timestamp;
+
+        $result = apbct_cookies_test();
+
+        $this->assertSame(1, $result, 'Cookie with md5(api_key + salt + timestamp) must pass validation');
+    }
+
+    /**
+     * Test that check_value with timestamp but WITHOUT salt is rejected.
+     */
+    public function testApbctCookiesTestRejectsTimestampCookieWithoutSalt()
+    {
+        global $apbct;
+
+        $timestamp = '1718000000';
+
+        $cookie_test_value = array(
+            'cookies_names' => array('ct_ps_timestamp'),
+            'check_value'   => md5($apbct->api_key . $timestamp), // No salt
+        );
+
+        $cookie_prefix = function_exists('apbct__get_cookie_prefix') ? apbct__get_cookie_prefix() : '';
+        $_COOKIE[$cookie_prefix . 'apbct_cookies_test'] = urlencode(json_encode($cookie_test_value));
+        $_COOKIE[$cookie_prefix . 'ct_ps_timestamp'] = $timestamp;
+
+        $result = apbct_cookies_test();
+
+        $this->assertSame(0, $result, 'Cookie with md5(api_key + timestamp) without salt must be rejected');
+    }
+}