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# lab-1

## Modifying Serialized Objects

**Difficulty:** Apprentice

### Lab Description

This lab uses a serialization-based session mechanism and is vulnerable to privilege escalation.

**Objective:** Edit the serialized object in the session cookie to gain administrative privileges, then delete the user `carlos`.

**Credentials:** `wiener:peter`

### Root Cause

PHP uses a mostly human-readable string format for serialization, with letters representing the data type and numbers representing the length of each entry. For example, a `User` object with the attributes:

```php
$user->name = "carlos";
$user->isLoggedIn = true;
```

When serialized, looks like:

```
O:4:"User":2:{s:4:"name";s:6:"carlos";s:10:"isLoggedIn";b:1;}
```

This serialized object can be stored anywhere — browser cookies, local storage, session — in any encoded format (such as Base64) within the HTTP request. Anyone can decode it, identify it as a PHP serialized object, modify its values, and send it back to the server. If the server blindly trusts and deserializes the modified object without checking whether it was legitimately generated by the application, the attacker gets whatever access the modified data grants. This leads to account takeover, access control bypass, and privilege escalation.

### Exploitation

1. Start the login flow as `wiener:peter`.
2. After login, inspect the session cookie — in the browser's Network tab or Burp, URL-decode it, then Base64-decode it to reveal the raw PHP serialized object.
3. Find the `isAdmin` attribute and change `b:0` to `b:1`.
4. Re-encode the modified object: Base64-encode it, then URL-encode the result.
5. Replace the session cookie with the modified value and reload the page.
6. The admin panel is now accessible — delete `carlos` to complete the lab.

### Lesson Learned

The server must verify — before deserializing — that the serialized object was legitimately generated by the application. Never blindly trust user-controlled objects. If serialized data must be stored client-side, protect it with cryptographic integrity (for example, an HMAC or authenticated encryption) so that any modification can be detected before deserialization occurs.


---

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