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:
References
kurt-r2c Analyst
Incorrect Access Control in
file_method?inlib/simple_form/form_builder.rb; a user-supplied string is invoked as a method callImpact
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:
The string provided in the variable
@user_supplied_stringwould be invoked as a method call inside the@userobject (unless the string contains any of the following:password,time_zone,country,email,phoneandurl).By manipulation that input, an attacker could do any of the following:
#destroy)Patches
The problem was fixed in version
5.0. Although it's a major version, there should be no issues with upgrading for4.x. The reason it was released in a major version is that the configurationSimpleForm.file_methodswas 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
asoption, like the following:References
[TDB]
For more information
If you have any questions or comments about this advisory:
References