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Fencer Vulns
medium 5.3

CVE-2025-54121 json

Starlette has possible denial-of-service vector when parsing large files in multipart forms

published 2025-07-21 15 mo ago modified 2026-09-10 1 mo ago also EUVD-2025-22159 , GHSA-2c2j-9gv5-cj73 , PYSEC-2026-1941

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 51%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi starlette 0.47.2
  • encode starlette 0.47.2
  • kludex starlette 0.47.2
  • starlette Debian 12 0.26.1-1+deb12u1
  • starlette Debian 14, Debian 13 0.46.1-3

debian advisories DEBIAN-CVE-2025-54121

  • python-starlette SLES for SAP applications 16.0, SLES 16.0 0.41.3-160000.3.1
  • python-starlette openSUSE Leap 15.6 0.35.1-150600.3.6.1

suse advisories SUSE-SU-2026:22151-1SUSE-SU-2025:02544-1

  • python-starlette openSUSE Leap 16.0 0.41.3-160000.3.1
  • python-starlette openSUSE Tumbleweed 0.47.2-1.1

opensuse advisories openSUSE-SU-2026:20975-1openSUSE-SU-2025:15381-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-54121 updated cvss 5.3

starlette: Starlette denial-of-service

  • Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-service-api-rhel9 Red Hat AI Inference Server rhaiis/vllm-cuda-rhel9, rhaiis/vllm-rocm-rhel9 Red Hat Ansible Automation Platform 2 ansible-automation-platform-24/de-minimal-rhel8, ansible-automation-platform-24/de-minimal-rhel9, ansible-automation-platform-25/de-minimal-rhel8, ansible-automation-platform-25/de-minimal-rhel9, ansible-automation-platform-24/ee-supported-rhel8, ansible-automation-platform-24/ee-supported-rhel9, +5 more Red Hat Enterprise Linux AI (RHEL AI) rhelai1/gemma-2-9b-it, rhelai1/bootc-amd-rhel9, rhelai1/bootc-intel-rhel9, rhelai1/gemma-2-9b-it-fp8, rhelai1/skills-adapter-v3, rhelai1/bootc-nvidia-rhel9, +24 more Red Hat OpenShift AI (RHOAI) rhoai/odh-rhel8-operator, rhoai/odh-dashboard-rhel8, rhoai/odh-modelmesh-rhel8, rhoai/odh-mm-rest-proxy-rhel8, rhoai/odh-mm-rest-proxy-rhel9, rhoai/odh-feast-operator-rhel9, +44 more Red Hat Satellite 6 satellite/iop-advisor-engine-rhel9
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
15 mo ago

Exploit prediction

0.66% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
pypi starlette
<0.47.2
0.47.2

Affected products

  • encode starlette

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.