CVE-2025-62727 — Inefficient Algorithmic Complexity in Starlette

CWE-407 — Inefficient Algorithmic ComplexityCWE-400 — Uncontrolled Resource Consumption6 documents5 sources
Severity
7.5HIGHNVD
EPSS
0.4%
top 39.37%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
3
Encode StarletteDebian StarletteKludex Starlette
Timeline
PublishedOct 28

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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HExploitability: 3.9 | Impact: 3.6

Affected Packages4 packages

▶PyPIencode/starlette0.39.0 — 0.49.1
▶debiandebian/starlette< starlette 0.50.0-1 (forky)
▶Debianencode/starlette< 0.46.1-3+deb13u1+1
▶CVEListV5kludex/starlette>= 0.39.0, < 0.49.1

🔴Vulnerability Details

3
OSV
CVE-2025-62727: Starlette is a lightweight ASGI framework/toolkit↗2025-10-28
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GHSA
Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``↗2025-10-28
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OSV
Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``↗2025-10-28
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📋Vendor Advisories

2
Red Hat
starlette: Starlette DoS via Range header merging↗2025-10-28
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Debian
CVE-2025-62727: starlette - Starlette is a lightweight ASGI framework/toolkit. Starting in version 0.39.0 an...↗2025
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