Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header_CVE-2026-34230

{
    "lastseen": "",
    "description": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.select_best_encoding processes Accept-Encoding values with quadratic time complexity when the header contains many wildcard (*) entries. Because this method is used by Rack::Deflater to choose a response encoding, an unauthenticated attacker can send a single request with a crafted Accept-Encoding header and cause disproportionate CPU consumption on the compression middleware path. This results in a denial of service condition for applications using Rack::Deflater. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.",
    "published": "2026-04-02T16:41:21.095Z",
    "modified": "2026-04-03T18:19:00.388Z",
    "type": "cve",
    "title": "Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header",
    "source": "GitHub_M",
    "references": "https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr",
    "id": "CVE-2026-34230",
    "bulletinFamily": "",
    "cwe": [
        "CWE-400",
        "CWE-407"
    ],
    "cvelist": null,
    "sourceData": "rack rack < 2.2.23\nrack rack >= 3.0.0.beta1, < 3.1.21\nrack rack >= 3.2.0, < 3.2.6",
    "sourceHref": "",
    "cvss": {
        "score": 5.3,
        "severity": "MEDIUM",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
        "version": "3.1"
    },
    "cvss2": [],
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        "baseScore": 0,
        "baseSeverity": "",
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        "attackComplexity": "",
        "privilegesRequired": "",
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        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
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    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "rack",
    "version": "< 2.2.23",
    "vendor": "rack",
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    "ai_score": 0
}