Issue #3441726 by Grevil: Undefined array key 2 in Drupal\friendlycaptcha\SiteVerify->verify() when using local endpoint

Closes #3441726

src/SiteVerify.php

@@ -167,7 +167,12 @@ class SiteVerify {
     if (empty($solution)) {
       return self::returnErrorEmptySolution();
     }
-    [$signature, $puzzle, $solutions] = explode('.', $solution);
+    $solutionArray = explode('.', $solution);
+    if (count($solutionArray) !== 3) {
+      $this->logger->critical('The solution is malformed. Expected 3 parts, got %count', ['%count' => count($solutionArray)]);
+      return self::returnMalformedSolution();
+    }
+    [$signature, $puzzle, $solutions] = $solutionArray;
     $puzzleBin = base64_decode($puzzle);
     $puzzleHex = bin2hex($puzzleBin);
     if (($calculated = self::signBuffer($puzzleBin, $this->config->get('site_key'))) !== $signature) {
@@ -250,6 +255,16 @@ class SiteVerify {
     return self::returnResponse(FALSE, 'solution_missing');
   }
 
+  /**
+   * Helper function to return a response array for a malformed solution.
+   *
+   * @return array
+   *   The response array for a malformed solution.
+   */
+  private static function returnMalformedSolution(): array {
+    return self::returnResponse(FALSE, 'solution_malformed');
+  }
+
   /**
    * Helper function to prepare the response array.
    *