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[Security] [csrf] Add documentation about breach #14875

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Jan 26, 2021
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[Security] [csrf] Add documentation about breach #14875

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17 changes: 16 additions & 1 deletion security/csrf.rst
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Expand Up @@ -85,7 +85,7 @@ this can be customized on a form-by-form basis::

// src/Form/TaskType.php
namespace App\Form;

// ...
use App\Entity\Task;
use Symfony\Component\OptionsResolver\OptionsResolver;
Expand Down Expand Up @@ -162,4 +162,19 @@ to check its validity::
}
}

CSRF Tokens and Compression Side-Channel Attacks
------------------------------------------------

`BREACH`_ and `CRIME`_ are security exploits against HTTPS when using HTTP
compression. Attacker can leverage information leaked by compression to recover
targeted parts of the plaintext. To mitigate these attacks, and prevent an
attacker from guessing the CSRF tokens, a random mask is prepended to the token
and used to scramble it.

.. versionadded:: 5.3

The randomization of tokens was introduced in Symfony 5.3

.. _`Cross-site request forgery`: https://en.wikipedia.org/wiki/Cross-site_request_forgery
.. _`BREACH`: https://en.wikipedia.org/wiki/BREACH
.. _`CRIME`: https://en.wikipedia.org/wiki/CRIME