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POWhy is using thread locals in Django bad?
 

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  1. POWhy is using thread locals in Django bad?
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    <p>I am using thread locals to store the current user and request objects. This way I can have easy access to the request from anywhere in the programme (e.g. dynamic forms) without having to pass them around.</p> <p>To implement the thread locals storage in a middleware, I followed a tutorial on the Django site: <a href="http://code.djangoproject.com/wiki/CookBookThreadlocalsAndUser?version=18" rel="noreferrer">http://code.djangoproject.com/wiki/CookBookThreadlocalsAndUser?version=18</a></p> <p>This document has since been modified to suggest avoiding this technique: <a href="http://code.djangoproject.com/wiki/CookBookThreadlocalsAndUser?version=20" rel="noreferrer">http://code.djangoproject.com/wiki/CookBookThreadlocalsAndUser?version=20</a></p> <p>From the article:</p> <blockquote> <p>From a design point of view, threadlocals are essentially global variables, and are subject to all the usual problems of portability and predictability that global variables usually entail.</p> <p>More importantly, from a security point of view, threadlocals pose a huge risk. By providing an data store that exposes the state of other threads, you provide a way for one thread in your web server to potentially modify the state of another thread in the system. If the threadlocal data contains descriptions of users or other authentication-related data, that data could be used as the basis for an attack that grants access to an unauthorized user, or exposes private details of a user. While it is possible to build a threadlocal system that is safe from this sort of attack, it's a lot easier to be defensive and build a system that isn't subject to any such vulnerability in the first place.</p> </blockquote> <p>I understand why global variables can be bad, but in this case I'm running my own code on my own server so I can't see what danger two global variables pose.</p> <p>Can someone explain the security issue involved? I have asked many people how they would hack my application if they read this article and know I'm using thread locals, yet no one has been able to tell me. I am starting to suspect that this is an opinion held by hair-splitting purists who love to pass objects explicitly.</p>
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    1. USNick Bastin
    1. UShekevintran
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      1. USValentin Golev
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    1. COBy the way - do you have the original example? It's deleted now and I want to use that...
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    2. COThis snippet is pretty similar to the deleted page: http://djangosnippets.org/snippets/2179/
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