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Fencer Vulns
low 3.7

CVE-2026-53537 json

Python-Multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters

published 2026-06-15 4 mo ago modified 2026-10-25 14 d ago also GHSA-vffw-93wf-4j4q , PYSEC-2026-3041 , EUVD-2026-38324

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 21%
public exploits
0
none known

Summary

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, parse_options_header parsed Content-Disposition (and Content-Type) headers with email.message.Message, which transparently applies RFC 2231/5987 decoding. The extended parameter syntax (filename*=charset'lang'value, name*=..., and the filename*0/filename*1 continuation form) is decoded and surfaced under the bare filename/name key, and overrides the plain parameter when both are present. RFC 7578 §4.2 explicitly forbids the filename* form in multipart/form-data. Components that follow RFC 7578, or that do not implement RFC 2231/5987 decoding for multipart/form-data (WAFs, proxies, gateways), may interpret such a header differently. An attacker can exploit that difference to smuggle a different field name or filename past an upstream inspector to the backend. This vulnerability is fixed in 0.0.30.

Patch / fix

  • pypi python-multipart 0.0.30
  • fastapiexpert python-multipart 0.0.30
  • python-multipart Debian 14 0.0.32-1

debian advisories DEBIAN-CVE-2026-53537

  • python-python-multipart SLES for SAP applications 16.0, SLES 16.0 0.0.20-160000.5.1

suse advisories SUSE-SU-2026:22372-1

  • python-python-multipart openSUSE Leap 16.0 0.0.20-160000.5.1
  • python-python-multipart openSUSE Tumbleweed 0.0.32-1.1

opensuse advisories openSUSE-SU-2026:21066-1openSUSE-SU-2026:11099-1

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-2026-53537 updated cvss 3.7

multipart: Python-Multipart: Information disclosure via header parsing discrepancy

  • Red Hat Exploit Intelligence exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-ocp-rag-rhel9, openshift-lightspeed/lightspeed-service-api-rhel9, openshift-lightspeed/lightspeed-agentic-sandbox-rhel9 Red Hat AI Inference Server rhaii/vllm-cpu-rhel9, rhaii/vllm-tpu-rhel9, rhaii/vllm-cuda-rhel9, rhaii/vllm-rocm-rhel9, rhaiis/vllm-cpu-rhel9, rhaiis/vllm-tpu-rhel9, +7 more Red Hat Ansible Automation Platform 2 ansible-automation-platform-26/mcp-tools-rhel9, ansible-automation-platform-27/mcp-tools-rhel9, ansible-automation-platform-25/lightspeed-chatbot-rhel8, ansible-automation-platform-26/lightspeed-chatbot-rhel9, ansible-automation-platform-27/lightspeed-chatbot-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-rocm-rhel9, rhelai3/bootc-gaudi-rhel9, rhelai3/bootc-aws-cuda-rhel9, rhelai3/bootc-gcp-cuda-rhel9, rhelai3/disk-image-cuda-rhel9, +2 more
    +3 more products
    Red Hat OpenShift AI (RHOAI) rhoai/odh-automl-rhel9, rhoai/odh-mlserver-rhel9, rhoai/odh-caikit-nlp-rhel9, rhoai/odh-vllm-gaudi-rhel9, rhoai/odh-kserve-agent-rhel9, rhoai/odh-kserve-router-rhel9, +8 more Red Hat OpenShift Virtualization 4 container-native-virtualization/ocp-virt-validation-checkup-rhel9 Red Hat Satellite 6 satellite/iop-vmaas-rhel9, satellite/foreman-mcp-server-rhel9, satellite/iop-advisor-engine-rhel9, satellite/iop-host-inventory-rhel9, satellite/iop-vulnerability-engine-rhel9
    affected: no fix available “Fix deferred”
  • Red Hat Lightspeed Core lightspeed-core/lightspeed-stack-rhel9 Red Hat Enterprise Linux command line assistant rhel-cla/rhel-knowledge-bridge-rhel10 Red Hat Hardened Images jaeger
    not affected: vulnerable code not present

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
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 21% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
OSV 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
GitHub 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
pypi python-multipart
<0.0.30
0.0.30

Affected products

  • Kludex python-multipart

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-436 Interpretation Conflict

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.