High

Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length

Type: advisorySources: OSV

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit. For file parts, the uploaded body is written directly to a temporary file on disk rather than being constrained by the buffered in-memory upload limit. An unauthenticated attacker can therefore stream an arbitrarily large multipart file upload and consume unbounded disk space. This results in a denial of service condition for Rack applications that accept multipart form data. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Products: Not specified
Affected versions: Not specified
Fixed versions: Not specified
CVEs: CVE-2026-34829
Confirmed fixed CVEs: Not specified
Updated in this feed: 4 Nov 2026, 23:21 UTC · Revision 1

Source evidence

Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length

core-osv · Original source

Published 2 Apr 2026, 16:46 UTC

osv:CVE-2026-34829

Complete source record

{
  "id": "90c35bedc3fdb84e32cc5fffcb1a81d4ef281f7cbb7e2ee0901cc3624b02b774",
  "url": "https://osv.dev/vulnerability/CVE-2026-34829",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length",
    "summary": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit. For file parts, the uploaded body is written directly to a temporary file on disk rather than being constrained by the buffered in-memory upload limit. An unauthenticated attacker can therefore stream an arbitrarily large multipart file upload and consume unbounded disk space. This results in a denial of service condition for Rack applications that accept multipart form data. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.",
    "evidence": "osv:CVE-2026-34829",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-34829",
      "aliases": [
        "CVE-2026-34829",
        "GHSA-8vqr-qjwx-82mw"
      ],
      "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": [
        {
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              "repo": "https://github.com/rack/rack",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
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                {
                  "fixed": "f2af0c8f869193fa7bb7d20b619b3003418e1055"
                },
                {
                  "introduced": "52901caf09ebcda879512a8605059963a49df55d"
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                {
                  "fixed": "ae8431120e66e92d1885ab8ec0a553d9cad5ec13"
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                {
                  "introduced": "b68251c03788ff39d4a4b25424df7360426e4afd"
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                {
                  "fixed": "e1f22fdbe99afd2126b6fbf05bb12399359574b7"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.2.23"
                      }
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                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*",
                    "range": [
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                        "introduced": "3.0.0"
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                      {
                        "fixed": "3.1.21"
                      }
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                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*",
                    "range": [
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                        "introduced": "3.2.0"
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                        "fixed": "3.2.6"
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          ],
          "versions": [
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            "v3.1.5",
            "v3.1.4",
            "v3.1.3",
            "v3.1.2",
            "v3.1.0",
            "v2.2.8",
            "v2.2.7",
            "v2.2.6.2",
            "v2.2.6.1",
            "v2.2.6",
            "v2.2.5",
            "2.2.4",
            "3.0.0",
            "2.2.3",
            "v2.2.2",
            "v2.2.1",
            "2.2.0",
            "2.1.0",
            "2.0.1",
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            "2.0.0.alpha",
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            "1.0",
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-34829.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:40.565356922Z",
      "provider": "osv",
      "references": [
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34829.json",
        "https://access.redhat.com/security/cve/CVE-2026-34829",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34829.json",
        "https://github.com/rack/rack/security/advisories/GHSA-8vqr-qjwx-82mw",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-34829",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2454488"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-400",
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34829.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-34829",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 507956,
  "published_at": "2026-04-02T16:46:47.357+00:00"
}