CVE-2025-62727

Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse

Published Oct 28, 2025 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-7f5h-v6xp-fcq8 Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``
History
Type Values Removed Values Added
Description Starlette is a lightweight ASGI framework/toolkit. Prior to 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. 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.
References
Type Values Removed Values Added
First Time appeared Encode
Encode starlette
Vendors & Products Encode
Encode starlette
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description Starlette is a lightweight ASGI framework/toolkit. Prior to 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.
Title Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse
Weaknesses CWE-407
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Nov 4, 2025, 5:41 PM
Reserved
Oct 20, 2025, 7:41 PM
Status
Deferred
Published
Oct 28, 2025, 9:15 PM
Modified
Oct 8, 2026, 11:10 AM
Severity
Important
Public date
Oct 28, 2025, 8:14 PM