> For the complete documentation index, see [llms.txt](https://infosecgirls.gitbook.io/infosecgirls-training/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://infosecgirls.gitbook.io/infosecgirls-training/appsec/some-attack-scenarios/4-customiterator.md).
# Custom Iterator
1. In Mutillidae, go to the login page by clicking on "Login/Register" link.
2. Ensure Burp is in intercept mode.
3. Click on "Please register here" link.
4\. Intercept the request and send it to Intruder.
5\. In "Intruder" > "Positions" tab, mark all positions where *user input* is expected.
6\. We intend to create unique users with user names like *user\_1*, *user\_2*, *user\_3*, and so on. Navigate to the `Payloads` sub-tab.
7\. Select the *payload set* corresponding to `username` field.
8\. Select *payload type* as `Custom Iterator`.
9\. Select `Position` as `1` and enter the static text **user** for *position 1*.
10\. Enter `_` (i.e., underscore) as the *separator* for position 1.
11\. Select `Position` as `2` and load a list of distinct values, say, numbers starting from 1 till 20.
12\. Navigate to the `Options` sub-tab. In `Grep - Extract` section, click on `Add` button.
13\. Click on `Refetch response`, and highlight the text that needs to be extracted from each of the server responses.
14\. Start the attack.
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