CVE-2026-53538
Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling
Description
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.
INFO
Published Date :
June 22, 2026, 4:56 p.m.
Last Modified :
June 22, 2026, 4:56 p.m.
Remotely Exploit :
Yes !
Source :
GitHub_M
Affected Products
The following products are affected by CVE-2026-53538
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | LOW | MITRE-CVE |
Solution
- Update Python-Multipart to version 0.0.30.
- Ensure upstream components are WHATWG compliant.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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CVE-2026-53538 vulnerability anywhere in the article.