Updates php/challenge-91.md

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Author: CHYbeta

SUMMARY.md

@@ -94,6 +94,7 @@
 * [Challenge 88](php/challenge-88.md)
 * [Challenge 89](php/challenge-89.md)
 * [Challenge 90](php/challenge-90.md)
+* [Challenge 91](php/challenge-91.md)
 
 ## RUBY
 

php/challenge-91.md

@@ -0,0 +1,22 @@
+# Challenge 
+```php
+<?php 
+if ($_SERVER['HTTP_X_FORWARDED_FOR'] === '127.0.0.1') {
+
+    echo "<br >Welcome My Admin ! <br >";
+
+    $pattern = $_GET[pat];
+    $replacement = $_GET[rep];
+    $subject = $_GET[sub];
+
+    if (isset($pattern) && isset($replacement) && isset($subject)) {
+        preg_replace($pattern, $replacement, $subject);
+    }else{
+        die();
+    }
+
+}
+?>
+```
+# Refference
++ 赛博地球杯工业互联网安全大赛 工控云管理系统设备维护中心被植入后门