Interpretation Conflict in python-multipart - CVE-2026-53538
Published: November 9, 2026
Vulnerability identifier: #VU162678
CSH Severity: Low
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-53538
CWE-ID: CWE-436
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to bypass upstream form validation by smuggling extra or overriding fields to a backend application.
The vulnerability exists due to python-multipart's QuerystringParser treating semicolons as separators in URL-encoded request bodies when an upstream inspecting component recognizes only ampersands. An unauthenticated remote attacker can submit a semicolon-delimited duplicate field that the backend interprets as an overriding value unseen by the upstream validator.
Affected software
python-multipart
How to mitigate CVE-2026-53538
Install security update from vendor's website.
python-multipart - update to 0.0.30