High severity · published Oct 28, 2025
CVE-2025-62727
Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse
7.5
CVSS
0.8%
EPSS
No
On KEV
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:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.8% · higher than 56% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ST
starlette · Kludex
>= 0.39.0, < 0.49.1 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-62727
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-62727
github.com
https://github.com/Kludex/starlette/commit/4ea6e22b489ec388d6004cfbca52dd5b147127c5
github.com
https://github.com/Kludex/starlette/commit/69ed26a85956ef4bd0161807eb27abf49be7cd3c
github.com
https://github.com/Kludex/starlette/releases/tag/0.49.1
github.com
https://github.com/Kludex/starlette/security/advisories/GHSA-7f5h-v6xp-fcq8
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