CVE-2026-53538

Summary

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.

Affected Software

Weaknesses

• CWE-436: CWE-436: Interpretation Conflict
• CWE-444: CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: partial

References

• https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m

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