High

ReDoS in multipart 1.3.0 - `parse_options_header()`

Type: advisorySources: OSV

multipart is a fast multipart/form-data parser for python. Prior to 1.2.2, 1.3.1 and 1.4.0-dev, 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. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.

Products: Not specified
Affected versions: Not specified
Fixed versions: Not specified
CVEs: CVE-2026-28356
Confirmed fixed CVEs: Not specified
Updated in this feed: 4 Nov 2026, 16:35 UTC · Revision 1

Source evidence

ReDoS in multipart 1.3.0 - `parse_options_header()`

core-osv · Original source

Published 12 Mar 2026, 16:45 UTC

osv:CVE-2026-28356

Complete source record

{
  "id": "25d8a2d517c8f272de42e4605855d44428eec248a06686002de334dae2bb5b7e",
  "url": "https://osv.dev/vulnerability/CVE-2026-28356",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ReDoS in multipart 1.3.0 - `parse_options_header()`",
    "summary": "multipart is a fast multipart/form-data parser for python. Prior to 1.2.2, 1.3.1 and 1.4.0-dev, 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. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.",
    "evidence": "osv:CVE-2026-28356",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-28356",
      "aliases": [
        "CVE-2026-28356",
        "GHSA-p2m9-wcp5-6qw3",
        "PYSEC-2026-2670"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/defnull/multipart",
              "type": "GIT",
              "events": [
                {
                  "introduced": "c43c0d5ad29423ae0d1ec544a360bc14016ea2df"
                },
                {
                  "fixed": "e6ef0a498233ddfa40f698451b31d58d57bf52c6"
                },
                {
                  "introduced": "0"
                },
                {
                  "fixed": "eeaff605f54386d3cda0674d025d28c23d632b40"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "1.3.0"
                      },
                      {
                        "fixed": "1.3.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.2.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.2.1",
            "v1.3.0",
            "v1.2.0",
            "v1.1.0",
            "v1.0.0",
            "v0.2.5",
            "v0.2.4",
            "v0.2.3",
            "v0.1",
            "v0.2.2",
            "0.2.2",
            "v0.2.1",
            "v0.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-28356.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:37.432178962Z",
      "provider": "osv",
      "references": [
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28356.json",
        "https://access.redhat.com/errata/RHSA-2026:10184",
        "https://access.redhat.com/errata/RHSA-2026:37275",
        "https://access.redhat.com/errata/RHSA-2026:42644",
        "https://access.redhat.com/errata/RHSA-2026:5809",
        "https://access.redhat.com/errata/RHSA-2026:6761",
        "https://access.redhat.com/errata/RHSA-2026:6762",
        "https://access.redhat.com/security/cve/CVE-2026-28356",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/28xxx/CVE-2026-28356.json",
        "https://github.com/defnull/multipart/security/advisories/GHSA-p2m9-wcp5-6qw3",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-28356",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2447059"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1333"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/28xxx/CVE-2026-28356.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-28356",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 504758,
  "published_at": "2026-03-12T16:45:01.07+00:00"
}