Date: Mon, 25 Jan 2016 11:37:57 -0800 From: Aaron Patterson <tenderlove@...y-lang.org> To: security@...e.de, rubyonrails-security@...glegroups.com, oss-security@...ts.openwall.com, ruby-security-ann@...glegroups.com Subject: [CVE-2016-0753] Possible Input Validation Circumvention in Active Model Possible Input Validation Circumvention in Active Model There is a possible input validation circumvention vulnerability in Active Model. This vulnerability has been assigned the CVE identifier CVE-2016-0753. Versions Affected: 4.1.0 and newer Not affected: 4.0.13 and older Fixed Versions: 5.0.0.beta1.1, 22.214.171.124, 126.96.36.199 Impact ------ Code that uses Active Model based models (including Active Record models) and does not validate user input before passing it to the model can be subject to an attack where specially crafted input will cause the model to skip validations. Vulnerable code will look something like this: ```ruby SomeModel.new(unverified_user_input) ``` Rails users using Strong Parameters are generally not impacted by this issue as they are encouraged to whitelist parameters and must specifically opt-out of input verification using the `permit!` method to allow mass assignment. For example, a vulnerable Rails application will have code that looks like this: ```ruby def create params.permit! # allow all parameters @user = User.new params[:users] end ``` Active Model and Active Record objects are not equipped to handle arbitrary user input. It is up to the application to verify input before passing it to Active Model models. Rails users already have Strong Parameters in place to handle white listing, but applications using Active Model and Active Record outside of a Rails environment may be impacted. All users running an affected release should either upgrade or use one of the workarounds immediately. Releases -------- The FIXED releases are available at the normal locations. Workarounds ----------- There are several workarounds depending on the application. Inside a Rails application, stop using `permit!`. Outside a Rails application, either use Hash#slice to select the parameters you need, or integrate Strong Parameters with your application. Patches ------- To aid users who aren't able to upgrade immediately we have provided patches for the two supported release series. They are in git-am format and consist of a single changeset. * 4-1-validation_skip.patch - Patch for 4.1 series * 4-2-validation_skip.patch - Patch for 4.2 series * 5-0-validation_skip.patch - Patch for 5.0 series Please note that only the 4.1.x and 4.2.x series are supported at present. Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases. Credits ------- Thanks to: [John Backus](https://github.com/backus) from BlockScore for reporting this! -- Aaron Patterson http://tenderlovemaking.com/ View attachment "4-1-validation_skip.patch" of type "text/plain" (3781 bytes) View attachment "4-2-validation_skip.patch" of type "text/plain" (3843 bytes) View attachment "5-0-validation_skip.patch" of type "text/plain" (4872 bytes) Content of type "application/pgp-signature" skipped
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