Security in Doctrine

When using Doctrine in a project it is always a security critical component because it talks directly to your database. As such security is very important to us. In security however, context is important and providing you with query capabilities we have to expose you to the risk of SQL injections.

Doctrine cannot prevent you from building SQL injections into your applications and so can no other DBAL, because it would require hiding SQL completely. But hiding SQL completly is not wanted, because it is such a powerful language.

Therefore it is still your responsibility to make sure that you are using Doctrine correctly when working with SQL.

But how would you know how to do so? Until now we had some small bits about security here and there in the documentation, mostly in the chapters about Query objects. We came to the conclusion that this is not enough.

That conclusion sinked in with a security issue we became aware of last month, where one Doctrine user reported that one of the core Doctrine\DBAL\Connection APIs is supposedly vulnerable to SQL injection. When you use $connection->insert($tableName, $values), then both the table name and the keys (columns) of the $values array are not escaped, because we assume they are never user input.

We evaluated this issue together with Padraic Brady (a known PHP security researcher) and came to the conclusion that this is not a security issue for us. Why? Because we don’t think this part of the API can be secured and trying will make our users feel safe, when they are not. Using the DBAL APIs directly always posed a much higher risk than using just the ORM.

You might think we are nuts by just claiming a non issue, but consider the assumptions we make about tables and columns and our reasoning:

  • Quoting identifiers is bad, because it changes them from case-insensitive to case-sensitive. Even more weird, Oracle unquoted identifiers are uppercased, PostgreSQL unquoted identifires are lowercased. MySQL casing is based on a config option. Doctrine 1.* had various unfixable bugs because of identifier quoting, which is why we decided that Doctrine will not use automatic identifier quoting.
  • The APIs of Connection#insert(), Connection#update() and Connection#delete() therfore accept both quoted and unquoted table/column identifiers, because quoting is the users choice.
  • A mechanism to detect SQL injection in strings that can be either quoted or unquoted is impossible to write completly secure. There are too many edge cases to consider and there is a realistic chance to miss one of them.
  • If you provide an API that is just secure in 99.999% of all cases, then you should not claim it is secure at all.

At this point you can still think we are wrong releasing insecure software, however let me ask back: Isn’t PHP shipping insecure software by providing PDO? SQL injection is possible by using PDO wrong. I can enumerate lots of libraries where security is the developers responsibility: Template engines, authentication libraries and so on.

A proper secured system requires knowledge about the context. That is why any kind of database abstraction layers can never fully protect you from SQL injection, because it does not know the context you are using it in.

To avoid secret knowledge about our security assumptions we are now starting to be completly explicit about these issues. Both DBAL and ORM now contain a SECURITY.md file, which contains basic information about security and links to much more detailed documentation chapters on Doctrine security.

We have made an effort to list all the functions and operations that are safe from SQL injection. There are not very many of them in the DBAL, because it is such a low level library. The ORM however is pretty secure, except when concatenating user input into DQL and SQL queries.

Read all the information about Security in Doctrine in the documentation.

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