CVE-2026-54019: Open WebUI: RAG ACL Bypass in Milvus Multitenancy Mode

This is a bypass of the fix for:

• GHSA-h36f-rqpx-j5wx
• CVE-2026-44560
• “Unauthorized File and Knowledge Base Content Access via RAG Vector Search”

Open WebUI added collection-level ACL checks, but the patch can still be bypassed when Milvus multitenancy mode is enabled. The ACL allows unknown non-KB collection names as legacy/ephemeral collections. In Milvus multitenancy mode, that user-controlled collection name becomes a resource_id and is interpolated into a Milvus expression without escaping.

An authenticated non-admin user can query:

x' or resource_id != '' or resource_id == 'x

This passes the Open WebUI ACL as an unknown collection, but Milvus evaluates:

resource_id == 'x' or resource_id != '' or resource_id == 'x'

That returns private knowledge-base chunks belonging to other users.