ChromaDB Python FastAPI server pre-auth RCE via embedding-function model loading before auth check (CVSS 4.0 = 10.0; v1.5.9 unpatched at disclosure)

HiddenLayer / Hadrian researchers disclosed CVE-2026-45829, a CVSS 4.0 = 10.0 pre-authentication RCE in ChromaDB's Python FastAPI server (affected from v1.0.0) (Hadrian Security, 2026-05-19; BleepingComputer, 2026-05-19). The vulnerable endpoint is POST /api/v2/tenants/{tenant}/databases/{db}/collections: when the request body sets trust_remote_code: true with an attacker-controlled HuggingFace model identifier (or a local path), the server fetches and executes the attacker-supplied Python code before the auth check fires, then politely returns 403 Forbidden after the code has run. The flaw exists only in the Python FastAPI server (chromadb[server] pip package) — the default Rust server (chroma run) does not traverse this code path. Per BleepingComputer's reporting of Shodan queries, approximately 73 % of internet-exposed ChromaDB instances are running a vulnerable version of the software. As of disclosure, ChromaDB v1.5.9 (latest) is unpatched. Mitigations: disable the Python FastAPI server and migrate to the Rust server; alternatively, block network-level access to the ChromaDB API (it should never be internet-exposed in the first place); if internal, set trust_remote_code: false server-wide via config. Detection concept — unexpected outbound network connections from ChromaDB Python server processes; child processes spawned by uvicorn / gunicorn workers with non-default lineage; access logs showing POST /api/v2/.../collections bodies referencing HuggingFace repository slugs with attacker-controlled patterns. T1190 Exploit Public-Facing Application; the impact maps to T1059.006 Python execution under the server context.