# CVE-2025-62727: PYSEC-2026-1942 - Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``

Source: https://junglewise.ai/threats/cve-2025-62727-starlette-vulnerable-to-o-n-2-dos-via-range-header-merging-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-10-28  
License: CC BY 4.0 with a link back

CVE-2025-62727 · Severity: high · CVSS 7.5 · Published 2025-10-28

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.

Technologies: [starlette (PyPI)](https://junglewise.ai/threats/technologies/pypi-starlette). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2025-62727 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-62727 being exploited in the wild.

**How severe is CVE-2025-62727?** High severity, with a CVSS score of 7.5, published 28 October 2025.

**Which products and versions are affected?** starlette (PyPI) ECOSYSTEM:introduced=0.39.0,fixed=0.49.1.

**Is there a fix for CVE-2025-62727?** Yes. starlette (PyPI): upgrade to 0.49.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2025-62727?** Check whether you run starlette (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- starlette (PyPI): upgrade to 0.49.1 or later

  ```sh
  pip install "starlette>=0.49.1"
  ```


## Affected products

- starlette (PyPI) ECOSYSTEM:introduced=0.39.0,fixed=0.49.1

## Identifiers

- CVE-2025-62727
- GHSA-7f5h-v6xp-fcq8
- PYSEC-2026-1942

## Related threats

- [PYSEC-2026-1941 - Starlette has possible denial-of-service vector when parsing large files in multipart forms](https://junglewise.ai/threats/cve-2025-54121-starlette-denial-of-service-in-multipart-form-parsing)
- [PYSEC-2026-1943 - Starlette Denial of service (DoS) via multipart/form-data](https://junglewise.ai/threats/cve-2024-47874-starlette-denial-of-service-dos-via-multipart-form-data)
- [Starlette denial of service via resource limit bypass in request.form](https://junglewise.ai/threats/cve-2026-54283-starlette-denial-of-service-via-resource-limit-bypass-in-request)
- [Kludex Starlette hostname spoofing via unvalidated request path](https://junglewise.ai/threats/cve-2026-54282-kludex-starlette-hostname-spoofing-via-unvalidated-request-path)
- [Starlette unsafe reflection in HTTPEndpoint method dispatching](https://junglewise.ai/threats/cve-2026-48817-starlette-unsafe-reflection-in-httpendpoint-method-dispatching)