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---
gem: activemodel
date: 2016-01-25
url: https://groups.google.com/forum/#!topic/rubyonrails-security/6jQVC1geukQ
cve: 2016-0753
title: Possible Input Validation Circumvention in Active Model
description: |
  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, 4.2.5.1, 4.1.14.1

  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!
unaffected_versions:
- "<= 4.0.13"
patched_versions:
- ">= 5.0.0.beta1.1"
- "~> 4.2.5, >= 4.2.5.1"
- "~> 4.1.14, >= 4.1.14.1"