Description
Starlette is a lightweight ASGI framework/toolkit. Starting in version 0.39.0 and prior to version 0.49.1 , an unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's FileResponse Range parsing/merging logic. This enables CPU exhaustion per request, causing denial‑of‑service for endpoints serving files (e.g., StaticFiles or any use of FileResponse). This vulnerability is fixed in 0.49.1.
References5
- github.com/Kludex/starlette/commit/4ea6e22b489ec388d6004cfbca52…
- github.com/Kludex/starlette/commit/69ed26a85956ef4bd0161807eb27…
- github.com/Kludex/starlette/releases/tag/0.49.1
- github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-…
- github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-…
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 57 · as of 10 November 2026
- CWE
- CWE-407
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.