CVE catalog

CVE-2026-53539

Python-Multipart is a streaming multipart parser for…

[CVE catalog]

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.

Severity
High · CVSS 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
Source
[NVD] · [CVE record]
EPSS
0.46% · Oct 27, 2026

Projects and upstream resources

Reported versions and fixes

Each observation applies to its named package, distribution, and release. Distribution backports can fix a vulnerability while retaining an older upstream version number.

Version impact has not been established. The original provider fields are retained below.

Provider details and historical evidence
Original provider fields
{
  "package_releases": [
    {
      "name": "python-multipart",
      "status": "fixed",
      "release": "sid",
      "version": "0.0.32-1"
    },
    {
      "name": "python-multipart",
      "status": "fixed",
      "release": "forky",
      "version": "0.0.32-1"
    },
    {
      "name": "python-multipart",
      "status": "vulnerable",
      "release": "trixie",
      "version": "0.0.20-1.1~deb13u1"
    },
    {
      "name": "python-multipart",
      "status": "vulnerable",
      "release": "bookworm",
      "version": "0.0.5-3"
    }
  ],
  "fixed_versions": [
    {
      "bug": 1140628,
      "name": "python-multipart",
      "type": "source",
      "origin": null,
      "release": "sid",
      "urgency": "not yet assigned",
      "fixed_version": "0.0.32-1"
    },
    {
      "bug": 1140628,
      "name": "python-multipart",
      "type": "source",
      "origin": null,
      "release": "forky",
      "urgency": "not yet assigned",
      "fixed_version": "0.0.32-1"
    },
    {
      "bug": 1140628,
      "name": "python-multipart",
      "type": "source",
      "origin": null,
      "release": "trixie",
      "urgency": "not yet assigned",
      "fixed_version": ""
    },
    {
      "bug": 1140628,
      "name": "python-multipart",
      "type": "source",
      "origin": null,
      "release": "bookworm",
      "urgency": "not yet assigned",
      "fixed_version": ""
    }
  ],
  "distribution_packages": [
    {
      "name": "python-multipart",
      "ecosystem": "cpe",
      "fixed_version": "not yet fixed"
    },
    {
      "name": "python-multipart",
      "ecosystem": "cpe",
      "fixed_version": "0.0.30"
    },
    {
      "name": "python-multipart",
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.0.30"
            }
          ]
        }
      ],
      "ecosystem": "PyPI",
      "fixed_version": "0.0.30",
      "provider_record_id": "GHSA-5RVQ-CXJ2-64VF"
    },
    {
      "name": "python-multipart",
      "ranges": [
        {
          "fixed": "0.0.30",
          "introduced": "",
          "last_affected": "",
          "start_excluding": ""
        }
      ],
      "ecosystem": "cpe",
      "fixed_version": "0.0.30",
      "provider_record_id": "NVD-CVE-2026-53539"
    }
  ]
}

[Debian bug #1140628]

Publisher notes

[trixie] python-multipart: Minor issue [bookworm] python-multipart: Minor issue; quadratic separator scan in QuerystringParser on ';'-separated urlencoded bodies

OpenFactory catalog packages

Matching against OpenFactory catalog package versions is in progress.

[Debian 12 (Bookworm)]

  • [python3-multipart]Unknown

    Source package: [python-multipart]

    Details (2)

    • 0.0.5-3 · all · bookworm

      Affected

      nvd · python-multipart · debian · bookworm; nvd · python-multipart · debian · 12

    • 0.0.5-3 · all · bookworm

      Affected

      nvd · python-multipart · debian · bookworm; nvd · python-multipart · debian · 12

[Debian 13 (Trixie)]

  • [python3-python-multipart]Unknown

    Source package: [python-multipart]

    Details (2)

    • 0.0.20-1.1~deb13u1 · all · trixie

      Affected

      nvd · python-multipart · debian · 13

    • 0.0.20-1.1~deb13u1 · all · trixie

      Affected

      nvd · python-multipart · debian · 13

Observed:

References

[Debian Security Tracker] · [FIRST EPSS] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX]