CVE-2026-53538Python-Multipart is a streaming multipart parser for Python.
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 3.7 LOW (v3.1, NVD)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- Weakness (CWE)
- CWE-436, CWE-444
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Jun 26, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
fastapiexpert python-multipart fastapiexpert:python-multipart | before 0.0.30 | NVD |
References
- https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599mvendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.