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CVE-2026-53538

CVE-2026-53538 · Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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 · EPSS 0.3% · Fix available

Published
Updated

Stack: system · python

Affected products and versions

  • python-multipart

    Versions
    • < 0.0.30: Affected

    No fix published

  • python-multipart Debian:12

    Versions
    • 0.0.17-1
    • 0.0.17-2
    • 0.0.17-3
    • 0.0.17-4
    • 0.0.17-5
    • 0.0.20-1
    • 0.0.20-1.1
    • 0.0.20-1.1~deb13u1
    • 0.0.22-1
    • 0.0.26-1
    • 0.0.32-1
    • 0.0.5-3
    • 0.0.6-1
    • 0.0.9-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-multipart Debian:13

    Versions
    • 0.0.20-1
    • 0.0.20-1.1
    • 0.0.20-1.1~deb13u1
    • 0.0.22-1
    • 0.0.26-1
    • 0.0.32-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-multipart Debian:14

    Versions
    • 0.0.20-1
    • 0.0.20-1.1
    • 0.0.20-1.1~deb13u1
    • 0.0.22-1
    • 0.0.26-1
    Affected ranges
    • ECOSYSTEM: < 0.0.32-1

    Update to 0.0.32-1

  • python-multipart PyPI

    Versions
    • 0.0.1
    • 0.0.10
    • 0.0.11
    • 0.0.12
    • 0.0.13
    • 0.0.14
    • 0.0.15
    • 0.0.16
    • 0.0.17
    • 0.0.18
    • 0.0.19
    • 0.0.2
    • 0.0.20
    • 0.0.21
    • 0.0.22
    • 0.0.23
    • 0.0.24
    • 0.0.25
    • 0.0.26
    • 0.0.27
    • 0.0.28
    • 0.0.29
    • 0.0.3
    • 0.0.4
    • 0.0.5
    • 0.0.6
    • 0.0.7
    • 0.0.8
    • 0.0.9
    Affected ranges
    • ECOSYSTEM: < 0.0.30

    Update to 0.0.30

  • python-multipart Ubuntu:Pro:22.04:LTS

    Versions
    • 0.0.5-2
    • 0.0.5-2ubuntu0.1~esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-multipart Ubuntu:Pro:24.04:LTS

    Versions
    • 0.0.5-3
    • 0.0.6-1
    • 0.0.9-1
    • 0.0.9-1ubuntu0.1~esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-multipart Ubuntu:25.10

    Versions
    • 0.0.20-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-multipart Ubuntu:26.10

    Versions
    • 0.0.20-1.1
    • 0.0.26-1
    • 0.0.32-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-multipart Ubuntu:26.04:LTS

    Versions
    • 0.0.20-1
    • 0.0.20-1.1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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