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CVE-2026-53538

20
FAUCET Score

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, QuerystringParser treated ; as a field separator in application/x-www-form-urlencoded bodies, in addition to &. The WHATWG URL standard, modern browsers, and Python's urllib.parse (since the CVE-2021-23336 fix) treat only & as a separator. This creates a parser differential: the same bytes are tokenized into different fields than a WHATWG compliant intermediary would produce, allowing an attacker to smuggle extra form fields past an upstream body inspecting component. This vulnerability is fixed in 0.0.30.

First published: Jun 22, 2026Last modified: Jun 22, 2026

Impacted Technologies

VendorProductVersion(s)CPE
< 0.0.30CPE matchmatch criteria
cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*

CVSS Data

CVSS version used by this source: 3.1

3.7LOW

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.18%
Probability of exploitation in next 30 days
EPSS Percentile
7.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0018 is in the 2nd percentile among its peer group of 1,506 CVEs.

Social Chatter

No social media mentions found for this CVE.

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.3 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

pippatch availablevia ghsa
Product: python-multipartFixed in: 0.0.30

Vendor Advisories (1)

pipGHSA-6jv3-5f52-599mlow

python-multipart: Semicolon treated as querystring field separator enables parameter smuggling

Jun 15, 2026

References

github.com / Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m
Vendor Advisory