hacktricks/pentesting-web/captcha-bypass.md

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# Captcha Bypass

To **automate** the **testing** of some functions of the server that allows user input it **could** be **needed** to **bypass** a **captcha** implementation. Test these things:

* **Do not send the parameter** related to the captcha.
  * Change from POST to GET or other HTTP Verbs
  * Change to JSON or from JSON
* Send the **captcha parameter empty**.
* Check if the value of the captcha is **in the source code** of the page.
* Check if the value is **inside a cookie.**
* Try to use an **old captcha value**
* Check if you can use the **same** captcha **value** several times with **the same or different sessionID.**
* If the captcha consists on a **mathematical operation** try to **automate** the **calculation.**
* If the captcha consists on **read characters from an image**, check manually or with code **how many images** are being used and if only a **few images are being used, detect them by MD5.**
* Use an **OCR** ([https://github.com/tesseract-ocr/tesseract](https://github.com/tesseract-ocr/tesseract)).


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