# LFI2RCE via PHP\_SESSION\_UPLOAD\_PROGRESS

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### Basic Info

If you found a **Local File Inclusion** even if you **don't have a session** and `session.auto_start` is `Off`. If **`session.upload_progress.enabled`** is **`On`** and you provide the **`PHP_SESSION_UPLOAD_PROGRESS`** in **multipart POST** data, PHP will **enable the session for you**.

```bash
$ curl http://127.0.0.1/ -H 'Cookie: PHPSESSID=iamorange'
$ ls -a /var/lib/php/sessions/
. ..
$ curl http://127.0.0.1/ -H 'Cookie: PHPSESSID=iamorange' -d 'PHP_SESSION_UPLOAD_PROGRESS=blahblahblah'
$ ls -a /var/lib/php/sessions/
. ..
$ curl http://127.0.0.1/ -H 'Cookie: PHPSESSID=iamorange' -F 'PHP_SESSION_UPLOAD_PROGRESS=blahblahblah'  -F 'file=@/etc/passwd'
$ ls -a /var/lib/php/sessions/
. .. sess_iamorange

In the last example the session will contain the string blahblahblah
```

Note that with **`PHP_SESSION_UPLOAD_PROGRESS`** you can **control data inside the session**, so if you includes your session file you can include a part you control (a php shellcode for example).

{% hint style="info" %}
Although most tutorials on the Internet recommends you to set `session.upload_progress.cleanup` to `Off` for debugging purpose. The default `session.upload_progress.cleanup` in PHP is still `On`. It means your upload progress in the session will be cleaned as soon as possible. So this will be **Race Condition**.
{% endhint %}

### The CTF

In the [**original CTF**](https://blog.orange.tw/2018/10/) where this technique is commented, it wasn't enough to exploit the Race Condition but the content loaded needed to start also with the string `@<?php`.

Due to the default setting of `session.upload_progress.prefix`, our **SESSION file will start with a annoying prefix** `upload_progress_` Such as: `upload_progress_controlledcontentbyattacker`

The trick to **remove the initial prefix** was to **base64encode the payload 3 times** and then decode it via `convert.base64-decode` filters, this is because when **base64 decoding PHP will remove the weird characters**, so after 3 times **only** the **payload** **sent** by the attacker will **remain** (and then the attacker can control the initial part).

More information in the original writeup [https://blog.orange.tw/2018/10/](https://blog.orange.tw/2018/10/) and final exploit [https://github.com/orangetw/My-CTF-Web-Challenges/blob/master/hitcon-ctf-2018/one-line-php-challenge/exp\_for\_php.py](https://github.com/orangetw/My-CTF-Web-Challenges/blob/master/hitcon-ctf-2018/one-line-php-challenge/exp\_for\_php.py)\
Another writeup in [https://spyclub.tech/2018/12/21/one-line-and-return-of-one-line-php-writeup/](https://spyclub.tech/2018/12/21/one-line-and-return-of-one-line-php-writeup/)

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