Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-53537Python-Multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters
Low 3.7
In plain English
A low-severity improper input validation in python-multipart from Kludex. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | python-multipart | no fix listed | DEBIAN-CVE-2026-53537 |
| Debian:14 | python-multipart | 0.0.32-1 | DEBIAN-CVE-2026-53537 |
| PyPI | python-multipart | 0.0.30 | GHSA-vffw-93wf-4j4q |
| PyPI | python-multipart | 0.0.30 | PYSEC-2026-3041 |
| Ubuntu:25.10 | python-multipart | no fix listed | UBUNTU-CVE-2026-53537 |
| Ubuntu:26.04:LTS | python-multipart | no fix listed | UBUNTU-CVE-2026-53537 |
| Ubuntu:26.10 | python-multipart | no fix listed | UBUNTU-CVE-2026-53537 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Kludex | python-multipart | < 0.0.30 |
Weakness: CWE-20, CWE-436 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N