CVE-2025-54121 | Starlette has possible denial-of-service vector when parsing large files in multipart forms

Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.

Published: 2025-07-21 Last update: 2026-04-15 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-54121 is rated Low Risk (37.5/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.25%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

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-2025-54121

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 0.89% 0.25% -0.64%
2 2026-05-17 0.20% 0.89% +0.68%
3 2026-04-09 — 0.20% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-54121

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L 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:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]

Weakness enumeration for CVE-2025-54121

GitHub Security Advisory for CVE-2025-54121

GHSA-2c2j-9gv5-cj73 · Severity: medium · Ecosystem: pip — Starlette has possible denial-of-service vector when parsing large files in multipart forms

OS Trackers for CVE-2025-54121

vendor priority summary link
debian not yet assigned CVE-2025-54121 not yet assigned priority: Debian including 1 source packages (starlette), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 1. https://security-tracker.debian.org/tracker/CVE-2025-54121
redhat medium — https://access.redhat.com/security/cve/CVE-2025-54121
suse medium CVE-2025-54121 severity moderate: SUSE including 4 source package names (python311-starlette-0.35.1-150600.3.6.1, python311-starlette-0.47.2-1.1, python312-starlette-0.47.2-1.1, python313-starlette-0.47.2-1.1), 4 product×package rows across 2 product lines (openSUSE Leap 15.6, openSUSE Tumbleweed): Fixed 4. https://www.suse.com/security/cve/CVE-2025-54121/
ubuntu medium CVE-2025-54121 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-2025-54121

Affected software / configurations for CVE-2025-54121

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-54121

cvelogic Threat Intelligence