Linq Injection – From Attacking Filters to Code Execution

Some of you (especially the .Net guys) might have heard of the query language Linq (Language Integrated Query) used by Microsoft .Net applications and web sites. It’s used to access data from various sources like databases, files and internal lists. It can internally transform the accessed data in application objects and provides filter mechanisms similar to SQL. As it is used directly inside the application source code, it will be processed at compile time and not interpreted at runtime. While this provides a great type safety and almost no attack surface for injection attacks (except from possible handling problems in the different backends), it is extremely difficult to implement a dynamic filter system (e.g. for datatables which should allow users to select the column to filter on). That’s probably the reason why Scott Guthrie (Executive Vice President of the Cloud and Enterprise group in Microsoft, also one of the founders of the .Net project) presented the System.Linq.Dynamic package as part of the VS-2008 samples in 2008. This library allows to build Linq queries at runtime and therefore simplify dynamic filters. But as you may know, dynamic interpretation of languages based on user input is most of the time not the best option….

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