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

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.

Published: 2025-10-28 Last update: 2026-04-15 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-62727 is rated Moderate Risk (41.3/100): CVSS High severity, with low exploitation likelihood (EPSS 0.14%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-62727

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-22 0.45% 0.14% -0.31%
2 2026-03-27 0.33% 0.45% +0.12%
3 2026-03-26 — 0.33% —

Full EPSS history (13 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-62727

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2025-62727

GitHub Security Advisory for CVE-2025-62727

GHSA-7f5h-v6xp-fcq8 · Severity: high · Ecosystem: pip — Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``

OS Trackers for CVE-2025-62727

vendor priority summary link
debian unimportant CVE-2025-62727 unimportant priority: Debian including 1 source packages (starlette), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2025-62727
redhat high — https://access.redhat.com/security/cve/CVE-2025-62727
suse high CVE-2025-62727 severity important: SUSE including 8 source package names (python-starlette, python311-sse-starlette-3.2.0-1.1, …), 8 product×package rows across 2 product lines (openSUSE Leap 15.6, openSUSE Tumbleweed): Fixed 6, Known Not Affected 2. https://www.suse.com/security/cve/CVE-2025-62727/
ubuntu medium CVE-2025-62727 medium priority: Ubuntu including 1 source packages (starlette), 5 status rows across 5 suites (jammy, noble, plucky, questing, upstream): needs-triage 4, ignored 1. https://ubuntu.com/security/CVE-2025-62727

Affected software / configurations for CVE-2025-62727

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-62727

cvelogic Threat Intelligence