Re: [Rails-core] strong parameters safety issue enables accidental mass assignment
>From my Android phone on T-Mobile. The first nationwide 4G network. Original message From: Prem Sichanugrist Date: 20/10/2014 18:07 (GMT-08:00) To: rubyonrails-core@googlegroups.com Cc: rubyonrails-core@googlegroups.com Subject: Re: [Rails-core] strong parameters safety issue enables accidental mass assignment We already have plans to make Parameters not inherited from Hash before Rails 4.2, but we couldn't do it because it breaks backward compatibility. What we did, instead, was to make sure we have test to cover those cases, and reimplement those methods that leaked Hash object. https://github.com/rails/rails/blob/v4.2.0.beta2/actionpack/test/controller/parameters/accessors_test.rb https://github.com/rails/rails/blob/v4.2.0.beta2/actionpack/test/controller/parameters/mutators_test.rb If we missed something, please let us know. After 4-2-stable has been cut out, and master becomes 5.0, then we'll make Parameters not inherited from Hash. Thanks, Prem On Thu, Aug 7, 2014 at 3:19 AM, Matt Jones wrote: On Aug 6, 2014, at 12:51 PM, johannes.schlumber...@appfolio.com wrote: [snip] Why does that matter? It matters because it is possible for a developer to accidentally lose that capability accidentally very easily on the way from the controller (where permit happened and the capability gets created) to the model (where the capability gets used). This loss does happen silently and effectively disables mass assignment protection. How does that happen? The only class aware of the 'permitted?' capability is ActiveController::Parameters, if we call a method that is not aware of the capability it can get lost as a side effect: class SomeModel < ActiveRecord::Base #fields :name, :protected_secret_field include ActiveModel::ForbiddenAttributesProtection end #imagine a request w/ params = {'name' => 1, 'protected_secret_field' => 2}: params.reject!{|k,_|['controller', 'action'].include? k} params.permit(:name) SomeModel.new(params) #Exception, world is OK SomeModel.new(params.symbolize_keys) #No Exception, secret overwritten This is a bug in `symbolize_keys`. It appears to have been fixed (accidentally? on purpose?) on master: https://github.com/rails/rails/commit/f1bad130d0c9bd77c94e43b696adca56c46a66aa by starting the loop with `self.class.new` instead of `{}`. There’s some additional future changes coming up in Ruby 2.2.0 with methods like `reject`: https://www.ruby-lang.org/en/news/2014/03/10/regression-of-hash-reject-in-ruby-2-1-1/ that seem likely to further complicate the situation. —Matt Jones -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-core+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-core@googlegroups.com. Visit this group at http://groups.google.com/group/rubyonrails-core. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-core+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-core@googlegroups.com. Visit this group at http://groups.google.com/group/rubyonrails-core. For more options, visit https://groups.google.com/d/optout.
Re: [Rails-core] strong parameters safety issue enables accidental mass assignment
We already have plans to make Parameters not inherited from Hash before Rails 4.2, but we couldn't do it because it breaks backward compatibility. What we did, instead, was to make sure we have test to cover those cases, and reimplement those methods that leaked Hash object. https://github.com/rails/rails/blob/v4.2.0.beta2/actionpack/test/controller/parameters/accessors_test.rb https://github.com/rails/rails/blob/v4.2.0.beta2/actionpack/test/controller/parameters/mutators_test.rb If we missed something, please let us know. After 4-2-stable has been cut out, and master becomes 5.0, then we'll make Parameters not inherited from Hash. Thanks, Prem On Thu, Aug 7, 2014 at 3:19 AM, Matt Jones wrote: > On Aug 6, 2014, at 12:51 PM, johannes.schlumber...@appfolio.com wrote: > [snip] >> >> Why does that matter? >> It matters because it is possible for a developer to accidentally lose that >> capability accidentally very easily on the way from the controller (where >> permit happened and the capability gets created) to the model (where the >> capability gets used). This loss does happen silently and effectively >> disables >> mass assignment protection. >> >> How does that happen? >> The only class aware of the 'permitted?' capability is >> ActiveController::Parameters, if we call a method that is not aware of the >> capability it can get lost as a side effect: >> >> class SomeModel < ActiveRecord::Base >> #fields :name, :protected_secret_field >> include ActiveModel::ForbiddenAttributesProtection >> end >> >> #imagine a request w/ params = {'name' => 1, 'protected_secret_field' => 2}: >> params.reject!{|k,_|['controller', 'action'].include? k} >> params.permit(:name) >> SomeModel.new(params) #Exception, world is OK >> SomeModel.new(params.symbolize_keys) #No Exception, secret overwritten >> > This is a bug in `symbolize_keys`. It appears to have been fixed > (accidentally? on purpose?) on master: > https://github.com/rails/rails/commit/f1bad130d0c9bd77c94e43b696adca56c46a66aa > by starting the loop with `self.class.new` instead of `{}`. > There’s some additional future changes coming up in Ruby 2.2.0 with methods > like `reject`: > https://www.ruby-lang.org/en/news/2014/03/10/regression-of-hash-reject-in-ruby-2-1-1/ > that seem likely to further complicate the situation. > —Matt Jones -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-core+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-core@googlegroups.com. Visit this group at http://groups.google.com/group/rubyonrails-core. For more options, visit https://groups.google.com/d/optout.
Re: [Rails-core] strong parameters safety issue enables accidental mass assignment
Hi everyone, I went ahead and made a strong_parameters compatible gem [1] whose Parameter class does not inherit from Hash anymore. It does not have any ancestors. The syntax for permit statements is identical to strong_parameters, the require feature is supported and parameters can be accessed in a Hash like syntax using the []-operator. We have used this gem for about a month now in some of our biggest rails apps without problems. My main concern, that I expressed when opening this thread, is resolved by this gem. If it is useful to the Rails Project or to anyone else, it is under MIT license. --Johannes [1] https://github.com/appfolio/shields_up -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-core+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-core@googlegroups.com. Visit this group at http://groups.google.com/group/rubyonrails-core. For more options, visit https://groups.google.com/d/optout.
Re: [Rails-core] strong parameters safety issue enables accidental mass assignment
On Aug 6, 2014, at 12:51 PM, johannes.schlumber...@appfolio.com wrote: [snip] > > Why does that matter? > It matters because it is possible for a developer to accidentally lose that > capability accidentally very easily on the way from the controller (where > permit happened and the capability gets created) to the model (where the > capability gets used). This loss does happen silently and effectively disables > mass assignment protection. > > How does that happen? > The only class aware of the 'permitted?' capability is > ActiveController::Parameters, if we call a method that is not aware of the > capability it can get lost as a side effect: > > class SomeModel < ActiveRecord::Base > #fields :name, :protected_secret_field > include ActiveModel::ForbiddenAttributesProtection > end > > #imagine a request w/ params = {'name' => 1, 'protected_secret_field' => 2}: > params.reject!{|k,_|['controller', 'action'].include? k} > params.permit(:name) > SomeModel.new(params) #Exception, world is OK > SomeModel.new(params.symbolize_keys) #No Exception, secret overwritten > This is a bug in `symbolize_keys`. It appears to have been fixed (accidentally? on purpose?) on master: https://github.com/rails/rails/commit/f1bad130d0c9bd77c94e43b696adca56c46a66aa by starting the loop with `self.class.new` instead of `{}`. There’s some additional future changes coming up in Ruby 2.2.0 with methods like `reject`: https://www.ruby-lang.org/en/news/2014/03/10/regression-of-hash-reject-in-ruby-2-1-1/ that seem likely to further complicate the situation. —Matt Jones signature.asc Description: Message signed with OpenPGP using GPGMail
Re: [Rails-core] strong parameters safety issue enables accidental mass assignment
Generally speaking I believe developers should be careful/responsible for handling what they are sending to their models for mass assignment, and there's where strong params help. The ideal solution indeed would be for Parameters not to inherit from Hash, which is something Rails will likely be changing in the near future. This would avoid people calling methods that are inherited from Hash in the Parameters object, such as symbolize_keys. It won't avoid people actually converting the Parameters object into a Hash with, say, a to_h/to_hash call, but at least that would make it more explicit. Thanks for sharing your thoughts on that. On Wed, Aug 6, 2014 at 1:51 PM, wrote: > Hello, > > Recently I was looking into upgrading one of our Rails 3.2 apps to use > strong_parameters. I encountered what seems like a flaw to me and I would > like > to spark discussion about this, hoping for personal learning and potential > improvement of the rails framework. > > The switch from protected attributes to strong parameters looks from the > outside > like access control for mass assignment moves from the model to the > controllers > (where, I agree, they belong). However looking at the implementation of > strong > parameters, it seems easy for developers to accidentally introduce bugs. > > How is that? > @params in a controller is of type ActiveController::Parameters, which > inherits > from HashWithIndifferentAccess which in turn inherits from a Ruby Hash. > Strong > Parameters extends ActiveController::Parameters to have a 'permitted?' > function, > essentially acting as the whitelist of permitted parameters for mass > assignment > [1]. > > Strong Parameters also overrides ActiveRecords sanitize_for_mass_assignment > function, where it checks if the attributes respond to 'permitted?'. The > implementation assumes that if the attributes Hash does not respond to > 'permitted?' the mass assignment decision should be deferred to > ActiveRecord. If > it responds to 'permitted?' and the mass assigned attributes are not on the > whitelist it will raise an exception [2]. > The 'permitted?' function here acts as a weird capability [3]. It is weird > because a capability that is not present will usually deny an action (mass > assignment) while here the action gets permitted in the absence of the > capability. > > Why does that matter? > It matters because it is possible for a developer to accidentally lose that > capability accidentally very easily on the way from the controller (where > permit happened and the capability gets created) to the model (where the > capability gets used). This loss does happen silently and effectively > disables > mass assignment protection. > > How does that happen? > The only class aware of the 'permitted?' capability is > ActiveController::Parameters, if we call a method that is not aware of the > capability it can get lost as a side effect: > > class SomeModel < ActiveRecord::Base > #fields :name, :protected_secret_field > include ActiveModel::ForbiddenAttributesProtection > end > > #imagine a request w/ params = {'name' => 1, 'protected_secret_field' => > 2}: > params.reject!{|k,_|['controller', 'action'].include? k} > params.permit(:name) > SomeModel.new(params) #Exception, world is OK > SomeModel.new(params.symbolize_keys) #No Exception, secret overwritten > > symbolize_keys returns an object of type Hash, that no longer has the > 'permitted?' function, so strong parameter protection is effectively > disabled. > > Both of these patterns are found quite a bit in our codebases - often in a > not > such simple form though. > > In some sense the problem is, that there is non-framework code on the > codepath between where the whitelist is defined and where it is used, and > it is > easy to accidentally lose the whitelist which disables mass assignment > protection. This problem did not exist with protected attributes, since > there > was no codepath. > > Using 'attr_accessible :name' on the model would have prevented these > problems, > however I am under the impression that strong_parameters is to replace > this old > way. > > Am I the only one worried about this (I have not found any discussion > online) or > is this a known problem? If it is known, what is the proposed solution? > I understand that developers need to take care when handling user input, > and > such should not call e.g. symbolize_keys. But the same is true for mass > assignment vulnerabilities as a whole - in a world where programmers do > not make > mistakes mass assignment errors do not exist. > > A possible solution could be to not attach this capability onto the > parameters > Hash but store it separately and then retrieve it at mass assignment time > - so > it is not the developers responsibility to babysit it. In an alternative > implementation 'permit/permit!' could be used to declare a list of mass > assignable parameters for a given action in a controller (optionally on a > per > model basis, default empty list)
[Rails-core] strong parameters safety issue enables accidental mass assignment
Hello, Recently I was looking into upgrading one of our Rails 3.2 apps to use strong_parameters. I encountered what seems like a flaw to me and I would like to spark discussion about this, hoping for personal learning and potential improvement of the rails framework. The switch from protected attributes to strong parameters looks from the outside like access control for mass assignment moves from the model to the controllers (where, I agree, they belong). However looking at the implementation of strong parameters, it seems easy for developers to accidentally introduce bugs. How is that? @params in a controller is of type ActiveController::Parameters, which inherits from HashWithIndifferentAccess which in turn inherits from a Ruby Hash. Strong Parameters extends ActiveController::Parameters to have a 'permitted?' function, essentially acting as the whitelist of permitted parameters for mass assignment [1]. Strong Parameters also overrides ActiveRecords sanitize_for_mass_assignment function, where it checks if the attributes respond to 'permitted?'. The implementation assumes that if the attributes Hash does not respond to 'permitted?' the mass assignment decision should be deferred to ActiveRecord. If it responds to 'permitted?' and the mass assigned attributes are not on the whitelist it will raise an exception [2]. The 'permitted?' function here acts as a weird capability [3]. It is weird because a capability that is not present will usually deny an action (mass assignment) while here the action gets permitted in the absence of the capability. Why does that matter? It matters because it is possible for a developer to accidentally lose that capability accidentally very easily on the way from the controller (where permit happened and the capability gets created) to the model (where the capability gets used). This loss does happen silently and effectively disables mass assignment protection. How does that happen? The only class aware of the 'permitted?' capability is ActiveController::Parameters, if we call a method that is not aware of the capability it can get lost as a side effect: class SomeModel < ActiveRecord::Base #fields :name, :protected_secret_field include ActiveModel::ForbiddenAttributesProtection end #imagine a request w/ params = {'name' => 1, 'protected_secret_field' => 2}: params.reject!{|k,_|['controller', 'action'].include? k} params.permit(:name) SomeModel.new(params) #Exception, world is OK SomeModel.new(params.symbolize_keys) #No Exception, secret overwritten symbolize_keys returns an object of type Hash, that no longer has the 'permitted?' function, so strong parameter protection is effectively disabled. Both of these patterns are found quite a bit in our codebases - often in a not such simple form though. In some sense the problem is, that there is non-framework code on the codepath between where the whitelist is defined and where it is used, and it is easy to accidentally lose the whitelist which disables mass assignment protection. This problem did not exist with protected attributes, since there was no codepath. Using 'attr_accessible :name' on the model would have prevented these problems, however I am under the impression that strong_parameters is to replace this old way. Am I the only one worried about this (I have not found any discussion online) or is this a known problem? If it is known, what is the proposed solution? I understand that developers need to take care when handling user input, and such should not call e.g. symbolize_keys. But the same is true for mass assignment vulnerabilities as a whole - in a world where programmers do not make mistakes mass assignment errors do not exist. A possible solution could be to not attach this capability onto the parameters Hash but store it separately and then retrieve it at mass assignment time - so it is not the developers responsibility to babysit it. In an alternative implementation 'permit/permit!' could be used to declare a list of mass assignable parameters for a given action in a controller (optionally on a per model basis, default empty list) and store it on the request or as a thread local variable. The mass_assignment part on the model would then read this variable and decide if the mass assignment should be allowed or not. This way the capability/whitelist can not be accidentally lost by transforming the parameters hash anymore. best, Johannes [1] https://github.com/rails/strong_parameters/blob/master/lib/action_controller/parameters.rb [2] https://github.com/rails/strong_parameters/blob/master/lib/active_model/forbidden_attributes_protection.rb [3] http://en.wikipedia.org/wiki/Capability-based_security -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-core+unsubscr...@googlegroups.com. To post to this group, send email to rub