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Low, CVSS 3.7amended

python-multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters

CVE-2026-53537GHSA-vffw-93wf-4j4q

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (python-multipart 0.0.30), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS
  • CVE-2026-53537: 0.29% estimated exploitation activity in the next 30 days; percentile 21.80 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary parseoptionsheader 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 filename0/filename1 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. Details Given both a plain and an extended parameter, the extended value won. For example: An inspector following RFC 7578 sees the field comment, while the returned value was name=role. The same applies to filenames: The…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-vffw-93wf-4j4q

  2. Revision 1 · created ·

    Published from osv record GHSA-vffw-93wf-4j4q

Agent brief

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# Patch Next advisory brief: CVE-2026-53537

Advisory: python-multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters
IDs: CVE-2026-53537, GHSA-vffw-93wf-4j4q
Record: https://patchnext.com/advisories/cve-2026-53537 (revision 2, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: python-multipart 0.0.30. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI python-multipart: affected < 0.0.30; fixed in 0.0.30

## Suggested inspection (read-only)
- `python -m pip show python-multipart`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on python-multipart.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-vffw-93wf-4j4q (OSV record GHSA-vffw-93wf-4j4q lists affected ranges: PyPI python-multipart >=0 <0.0.30 (fixed))
- Verified: https://github.com/advisories/GHSA-vffw-93wf-4j4q (GitHub-reviewed advisory GHSA-vffw-93wf-4j4q lists affected ranges: PyPI python-multipart >=0 <0.0.30)

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