> For the complete documentation index, see [llms.txt](https://ir0nstone.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ir0nstone.gitbook.io/notes/misc/scanf-bypasses.md).

# scanf Bypasses

Sometimes you want `scanf` to not read anything, but continue standard execution. By this I mean that it **takes** your input, but it doesn't store it in memory, leaving the stack or heap untouched.

This might be because you have a sequential or iterative OOB write, but there is a canary in the way. Alternatively, the location you are writing to is **uninitialized** but the data gets printed back and you want to leak pointers this way (e.g. [Control Room](https://app.hackthebox.com/challenges/Control%2520Room) on Hack The Box).

So, here are a few inputs for different specifiers that help bypass this! Please do let me know of any more.

<table><thead><tr><th width="378">Scanf Specifier</th><th>Bypass</th></tr></thead><tbody><tr><td><code>%d</code>, <code>%ld</code></td><td>negative sign <code>-</code></td></tr><tr><td><code>%f</code>, <code>%lf</code></td><td>decimal point/full stop <code>.</code></td></tr><tr><td></td><td></td></tr></tbody></table>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://ir0nstone.gitbook.io/notes/misc/scanf-bypasses.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.