CVE-2025-62727: Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``

October 28, 2025 (updated October 29, 2025)

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).

References

github.com/Kludex/starlette
github.com/Kludex/starlette/commit/4ea6e22b489ec388d6004cfbca52dd5b147127c5
github.com/Kludex/starlette/releases/tag/0.49.1
github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-fcq8
github.com/advisories/GHSA-7f5h-v6xp-fcq8
nvd.nist.gov/vuln/detail/CVE-2025-62727

Code Behaviors & Features

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