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Vulnerability · Published Oct 28, 2025 · Assigned by GitHub_M

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

High 7.5

In plain English

A high-severity security flaw in starlette from Kludex. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 57% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.8%top 43.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack tooling1Public PoC

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:13starlette0.46.1-3+deb13u1DEBIAN-CVE-2025-62727
Debian:14starlette0.50.0-1DEBIAN-CVE-2025-62727
PyPIstarlette0.49.1GHSA-7f5h-v6xp-fcq8
PyPIstarlette0.49.1PYSEC-2026-1942
Ubuntu:22.04:LTSstarletteno fix listedUBUNTU-CVE-2025-62727
Ubuntu:24.04:LTSstarletteno fix listedUBUNTU-CVE-2025-62727
Ubuntu:25.10starletteno fix listedUBUNTU-CVE-2025-62727
Ubuntu:26.04:LTSstarletteno fix listedUBUNTU-CVE-2025-62727
Ubuntu:26.10starletteno fix listedUBUNTU-CVE-2025-62727

Affected products (as reported)

VendorProductVersions
Kludex starlette >= 0.39.0, < 0.49.1

Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References