Unsafe Query Risk in Active Record

[Rafael Mendonça França <rafaelmfranca () gmail com>]

This advisory concerns a security risk in all supported versions of Active Record.  There is no patch to apply for this 
issue.

Due to the query API that Active Record supports, there is a risk of unsafe query generation in two scenarios.  
Databases with a table that contains a column with the same name as the table and queries with join aliases which 
conflict with column names could be vulnerable to an attack where the attacker can perform certain manipulations to the 
SQL queries generated by Rails.

Determining Vulnerability
-------------------------

A vulnerable application will either contain columns named identically to their table, or have column names which 
conflict with join aliases.

For example, if you had a model called SecurityToken, which contained an attribute called `security_tokens` then the 
following code could be manipulated to return additional records:

  SecurityToken.find_by_security_tokens(params[:security_tokens])

Due to the typical approach of pluralizing for tables and using singular names for columns, this kind of conflict is 
very unlikely.

The second scenario would be join aliases which conflict with a column name already in the query.  For instance suppose 
`users` has a denormalized column `contacts` which indicates how many times a user has been contacted, and a Contact 
record for each.  The following query could be manipulated to return additional records:

  User.joins(:contacts).where(contacts: params[:contacts])

Workarounds
-----------

The simple work around is to call to_s on the value from params:

  SecurityToken.find_by_security_tokens(params[:security_tokens].to_s)

  User.joins(:contacts).where(contacts: params[:contacts].to_s)
  
Alternatively, rename any columns which collide with table names or likely join aliases.

Future Fixes
------------

Unfortunately it is not possible to implement a reliable fix for this risk without breaking applications which rely on 
related functionality to build their queries.  Future releases of Rails will be able to address this, however that 
functionality will need to be built in the open and have a long beta period to flush out unanticipated edge cases.

Credits 
------- 

Thanks to Joe van Dyk and to Fraser Newton of Clio for reporting the issue to us.