File Content Disclosure in Action View

Impact ------ There is a possible file content disclosure vulnerability in Action View. Specially crafted accept headers in combination with calls to render file: can cause arbitrary files on the target server to be rendered, disclosing the file contents.

The impact is limited to calls to render which render file contents without a specified accept format. Impacted code in a controller looks something like this:

ruby class UserController < ApplicationController def index render file: "#{Rails.root}/some/file" end end

Rendering templates as opposed to files is not impacted by this vulnerability.

All users running an affected release should either upgrade or use one of the workarounds immediately.

Releases -------- The 6.0.0.beta3, 5.2.2.1, 5.1.6.2, 5.0.7.2, and 4.2.11.1 releases are available at the normal locations.

Workarounds ----------- This vulnerability can be mitigated by specifying a format for file rendering, like this:

ruby class UserController < ApplicationController def index render file: "#{Rails.root}/some/file", formats: [:html] end end

In summary, impacted calls to render look like this:

render file: "#{Rails.root}/some/file"

The vulnerability can be mitigated by changing to this:

render file: "#{Rails.root}/some/file", formats: [:html]

Other calls to render are not impacted.

Alternatively, the following monkey patch can be applied in an initializer:

ruby $ cat config/initializers/formatsfilter.rb frozenstringliteral: true

ActionDispatch::Request.prepend(Module.new do def formats super().select do |format| format.symbol || format.ref == "/" end end end)

Credits ------- Thanks to John Hawthorn <john@hawthorn.email> of GitHub

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