What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-10-28 · updated 2026-10-08
• Weakness: CWE-407

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.

Affected products

• Kludex starlette: from 0.39.0, < 0.49.1

References

• https://github.com/Kludex/starlette/commit/4ea6e22b489ec388d6004cfbca52dd5b147127c5
• https://github.com/Kludex/starlette/commit/69ed26a85956ef4bd0161807eb27abf49be7cd3c
• https://github.com/Kludex/starlette/releases/tag/0.49.1
• https://github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-fcq8
• https://github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-fcq8

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