Preventing Injection Attacks with Syntax Embeddings A Host and Guest Language Independent Approach

Software written in one language often needs to construct sen- tences in another language, such as SQL queries, XML output, or shell command invocations. This is almost always done using un- hygienic string manipulation, the concatenation of constants and client-supplied strings. A client can then supply specially crafted input that causes the constructed sentence to be interpreted in an unintended way, leading to an injection attack. We describe a more natural style of programming that yields code that is impervious to injections by construction. Our approach embeds the grammars of the guest languages (e.g., SQL) into that of the host language (e.g., Java) and automatically generates code that maps the embed- ded language to constructs in the host language that reconstruct the embedded sentences, adding escaping functions where appropriate. This approach is generic, meaning that it can be applied with rela- tive ease to any combination of host and guest languages.