PYSEC-2026-2670

Vulnerability from pysec - Published: 2026-07-13 14:36 - Updated: 2026-07-13 16:05
VLAI
Details

Summary

The parse_options_header() function in multipart.py uses a regular expression with an ambiguous alternation, which can cause exponential backtracking (ReDoS) when parsing maliciously crafted HTTP or multipart segment headers. This can be abused for denial of service (DoS) attacks against web applications using this library to parse request headers or multipart/form-data streams.

Impact

Any WSGI or ASGI application using multipart.parse_form_data() directly or indirectly (e.g. while parsing multipart/form-data streams) is vulnerable. The slow-down is significant enough to block request handling threads for multiple seconds per request.

Affected versions

All versions up to and including 1.3.0 are affected. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Impacted products
Name purl
multipart pkg:pypi/multipart
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "multipart",
        "purl": "pkg:pypi/multipart"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.2.2"
            },
            {
              "introduced": "1.3.0"
            },
            {
              "fixed": "1.3.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1",
        "0.1.1",
        "0.2",
        "0.2.1",
        "0.2.2",
        "0.2.3",
        "0.2.4",
        "0.2.5",
        "1.0.0",
        "1.1.0",
        "1.2.0",
        "1.2.1",
        "1.3.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-28356",
    "GHSA-p2m9-wcp5-6qw3"
  ],
  "details": "## Summary\n\nThe `parse_options_header()` function in `multipart.py` uses a regular expression with an *ambiguous alternation*, which can cause *exponential backtracking (ReDoS)* when parsing maliciously crafted HTTP or multipart segment headers. This can be abused for **denial of service (DoS)** attacks against web applications using this library to parse request headers or `multipart/form-data` streams.\n\n## Impact\n\nAny WSGI or ASGI application using `multipart.parse_form_data()` directly or indirectly (e.g. while parsing `multipart/form-data` streams) is vulnerable. The slow-down is significant enough to block request handling threads for multiple seconds per request.\n\n## Affected versions\n\nAll versions up to and including `1.3.0` are affected. The issue is fixed in `1.2.2`, `1.3.1` and `1.4.0-dev`.",
  "id": "PYSEC-2026-2670",
  "modified": "2026-07-13T16:05:00.097780Z",
  "published": "2026-07-13T14:36:42.599741Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/defnull/multipart/security/advisories/GHSA-p2m9-wcp5-6qw3"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-28356"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/defnull/multipart"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/multipart"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-p2m9-wcp5-6qw3"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "multipart vulnerable to ReDoS in `parse_options_header()`"
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.