CVE-2016-6317 (activerecord): Unsafe Query Generation Risk in Active Record

ADVISORIES

GEM

activerecord

FRAMEWORK

Ruby on Rails

SEVERITY

CVSS v3.x: 7.5 (High)

UNAFFECTED VERSIONS

< 4.2.0
>= 5.0.0

PATCHED VERSIONS

>= 4.2.7.1

DESCRIPTION

There is a vulnerability when Active Record is used in conjunction with JSON parameter parsing. This vulnerability is similar to CVE-2012-2660, CVE-2012-2694 and CVE-2013-0155.

Impact

Due to the way Active Record interprets parameters in combination with the way that JSON parameters are parsed, it is possible for an attacker to issue unexpected database queries with "IS NULL" or empty where clauses. This issue does not let an attacker insert arbitrary values into an SQL query, however they can cause the query to check for NULL or eliminate a WHERE clause when most users wouldn't expect it.

For example, a system has password reset with token functionality:

    unless params[:token].nil?
      user = User.find_by_token(params[:token])
      user.reset_password!
    end

An attacker can craft a request such that params[:token] will return [nil]. The [nil] value will bypass the test for nil, but will still add an "IN ('xyz', NULL)" clause to the SQL query.

Similarly, an attacker can craft a request such that params[:token] will return an empty hash. An empty hash will eliminate the WHERE clause of the query, but can bypass the nil? check.

Note that this impacts not only dynamic finders (find_by_*) but also relations (User.where(:name => params[:name])).

All users running an affected release should either upgrade or use one of the work arounds immediately. All users running an affected release should upgrade immediately. Please note, this vulnerability is a variant of CVE-2012-2660, CVE-2012-2694, and CVE-2013-0155. Even if you upgraded to address those issues, you must take action again.

If this chance in behavior impacts your application, you can manually decode the original values from the request like so:

`ActiveSupport::JSON.decode(request.body)`

Workarounds

This problem can be mitigated by casting the parameter to a string before passing it to Active Record. For example:

    unless params[:token].nil? || params[:token].to_s.empty?
      user = User.find_by_token(params[:token].to_s)
      user.reset_password!
    end

RubySec