Securing Enterprise RAG: Why Access Control Must Happen Before Retrieval

Most failures in retrieval-augmented generation systems begin at the retrieval stage rather than inside the language model, when unauthorized data gets pulled in. The article argues that pre-filtering results by user permissions is safer than post-filtering, since blocked chunks can otherwise still influence rankings, caches, logs, or prompts. Recommended controls include propagating user and tenant identity into search, tagging indexed chunks with access metadata, enforcing row-level security, isolating caches by permission context, and logging every retrieval decision. It also stresses that application-level authentication alone does not govern what a retriever can access, and that teams should prove compliance through prompt-assembly tracing and adversarial access tests.