{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "2.2.23"
              },
              {
                "introduced": "3.0.0"
              },
              {
                "fixed": "3.1.21"
              },
              {
                "introduced": "3.2.0"
              },
              {
                "fixed": "3.2.6"
              }
            ],
            "source": "CPE_RANGE"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "f2af0c8f869193fa7bb7d20b619b3003418e1055"
            },
            {
              "introduced": "52901caf09ebcda879512a8605059963a49df55d"
            },
            {
              "fixed": "ae8431120e66e92d1885ab8ec0a553d9cad5ec13"
            },
            {
              "introduced": "b68251c03788ff39d4a4b25424df7360426e4afd"
            },
            {
              "fixed": "e1f22fdbe99afd2126b6fbf05bb12399359574b7"
            }
          ],
          "repo": "https://github.com/rack/rack",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-q2ww-5357-x388"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-130",
      "CWE-135"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34831.json"
  },
  "details": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.",
  "id": "CVE-2026-34831",
  "modified": "2026-07-15T01:49:05.012718265Z",
  "published": "2026-04-02T16:43:08.762Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34831.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34831"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Rack: Content-Length mismatch in Rack::Files error responses"
}