Testing for NoSQL injection

This article is part of the new OWASP Testing Guide v4.

Back to the OWASP Testing Guide v4 ToC:
   https://www.owasp.org/index.php/OWASP_Testing_Guide_v4_Table_of_Contents
Back to the OWASP Testing Guide Project:
   https://www.owasp.org/index.php/OWASP_Testing_Project

Brief Summary

NoSQL databases provide looser consistency restrictions than traditional SQL databases. By requiring fewer relational constraints and consistency checks, NoSQL databases often offer performance and scaling benefits. Yet these databases are still potentially vulnerable to injection attacks, even if they aren't using the traditional SQL syntax. Because these NoSQL injection attacks may execute within a procedural[1] language , rather than in the declarative[2] SQL language, the potential impacts are greater than traditional SQL injection.

Description of the Issue

NoSQL database calls are written in the application's programming language, a custom API call, or formatted according to a common convention (such as XML, JSON, LINQ, etc). Malicious input targeting those specifications may not trigger the primarily application sanitization checks. For example, filtering out common HTML special characters such as < > & ; will not prevent attacks against a JSON API, where special characters include / { } : .

There are now over 150 NoSQL databases available[3] for use within an application, providing APIs in a variety of languages and relationship models. Each offers different features and restrictions. Because there is not a common language between them, example injection code will not apply across all NoSQL databases. For this reason, anyone testing for NoSQL injection attacks will need to familiarize themselves with the syntax, data model, and underlying programming language in order to craft specific tests.

NoSQL injection attacks may execute in different areas of an application than traditional SQL injection. Where SQL injection would execute within the database engine, NoSQL variants may execute during within the application layer or the database layer, depending on the NoSQL API used and data model. Typically NoSQL injection attacks will execute where the attack string is parsed, evaluated, or concatenated into a NoSQL API call.

Additional timing attacks may be relevant to the lack of concurrency checks within a NoSQL database. These are not covered under injection testing.

At the time of writing MongoDB is the most widely used NoSQL database, and so all examples will feature MongoDB APIs.

Black Box testing and example

Testing for NoSQL injection vulnerabilities in MongoDB:
The MongoDB API expects BSON (Binary JSON) calls, and includes a secure BSON query assembly tool. However, according to MongoDB documentation - unserialized JSON and JavaScript expressions are permitted in several alternative query parameters.[4] The most commonly used API call allowing arbitrary JavaScript input is the $where operator.

The MongoDB $where operator typically is used as a simple filter or check, as it is within SQL.

db.myCollection.find( { $where: "this.credits == this.debits" } );

Optionally JavaScript is also evaluated to allow more advanced conditions.

db.myCollection.find( { $where: function() { return obj.credits - obj.debits < 0; } } );

If an attacker were able to manipulate the data passed into the $where operator, that attacker could include arbitrary JavaScript to be evaluated as part of the MongoDB query. An example vulnerability is exposed in the following code, if user input is passed directly into the MongoDB query without sanitization.

db.myCollection.find("{ $where: 'this.credits > " + userinput + "' }");

With normal SQL injection, a similar vulnerability would allow an attacker to execute arbitrary SQL commands - exposing or manipulating data at will. However, because JavaScript is a fully featured language, not only does this allow an attacker to manipulate data, but also to run arbitrary code.

Result Expected:
...

References

Whitepapers
http://blogs.adobe.com/asset/files/2011/04/NoSQL-But-Even-Less-Security.pdf

http://erlend.oftedal.no/blog/?blogid=110

http://seclists.org/fulldisclosure/2011/Dec/383

https://media.blackhat.com/bh-us-11/Sullivan/BH_US_11_Sullivan_Server_Side_WP.pdf

http://docs.mongodb.org/manual/faq/developers/#how-does-mongodb-address-sql-or-query-injection ...
Tools
...