CVE-2019-16676 — Improper Input Validation in simple_form — CVE...

## 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: ```erb <%= 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: ```erb <%= 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](https://github.com/plataformatec/simple_form) * Email us at [opensource@plataformatec.com.br](mailto:opensource@plataformatec.com.br)