Why is JsonRequestBehavior needed?

Question

Why is Json Request Behavior needed?

If I want to restrict the HttpGet requests to my action I can decorate the action with the [Http

Answer 1

MVC defaults to DenyGet to protect you against a very specific attack involving JSON requests to improve the liklihood that the implications of allowing HTTP GET exposure are considered in advance of allowing them to occur.

This is opposed to afterwards when it might be too late.

Note: If your action method does not return sensitive data, then it should be safe to allow the get.

Further reading from my Wrox ASP.NET MVC3 book

By default, the ASP.NET MVC framework does not allow you to respond to an HTTP GET request with a JSON payload. If you need to send JSON in response to a GET, you'll need to explicitly allow the behavior by using JsonRequestBehavior.AllowGet as the second parameter to the Json method. However, there is a chance a malicious user can gain access to the JSON payload through a process known as JSON Hijacking. You do not want to return sensitive information using JSON in a GET request. For more details, see Phil's post at http://haacked.com/archive/2009/06/24/json-hijacking.aspx/ or this SO post.

Haack, Phil (2011). Professional ASP.NET MVC 3 (Wrox Programmer to Programmer) (Kindle Locations 6014-6020). Wrox. Kindle Edition.

Related StackOverflow question

With most recents browsers (starting with Firefox 21, Chrome 27, or IE 10), this is no more a vulnerability.