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GHSA-r74q-gxcg-73hx
No affected components available
Incorrect Access Control in file_method? in lib/simple_form/form_builder.rb; a user-supplied string is invoked as a method call
Impact
For pages that build a form using user input, it is possible for an attacker to manipulate the input and send any method present in the form object. For example:
<%= simple_form_for @user do |f| %>
<%= f.label @user_supplied_string %>
...
<% end %>
The string provided in the variable @user_supplied_string would be invoked as a method call inside the @user object (unless the string contains any of the following: password, time_zone, country, email, phone and url).
By manipulation that input, an attacker could do any of the following:
- Code execution (call actions like
#destroy) - Denial of Service (by executing a computation intensive method)
- Information Disclosure (check the presence of methods, leak user information)
Patches
The problem was fixed in version 5.0. Although it's a major version, there should be no issues with upgrading for 4.x. The reason it was released in a major version is that the configuration SimpleForm.file_methods was deprecated in order to fix the problem.
Workarounds
The issue only happens with pages that build forms based on user-provided input. If your application doesn't do that, you're not affected.
A workaround is to explicitly pass which type you want for an input since the issue lies on Simple Form's automatically discovery of input types. This can be done using the as option, like the following:
<%= form.input :avatar, as: :file %>
References
[TDB]
For more information
If you have any questions or comments about this advisory:
- Open an issue in https://github.com/plataformatec/simple_form
- Email us at opensource@plataformatec.com.br
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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