Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy_CVE-2026-32688

{
    "lastseen": "",
    "description": "Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion.\n\nPlug.Cowboy.Conn.conn/1 in lib/plug/cowboy/conn.ex calls String.to_atom/1 on the value returned by :cowboy_req.scheme/1. For HTTP/2 connections, cowlib passes the client-supplied :scheme pseudo-header value through verbatim without validation. Each unique value permanently allocates a new entry in the BEAM atom table. Since atoms are never garbage-collected and the atom table has a fixed limit (default 1,048,576), an unauthenticated attacker can exhaust the table by sending HTTP/2 requests with unique :scheme values, causing the Erlang VM to abort with system_limit and taking down the entire node.\n\nThis vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header.\n\nThis issue affects plug_cowboy: from 2.0.0 before 2.8.1.",
    "published": "2026-04-27T13:45:35.160Z",
    "modified": "2026-04-27T13:45:35.160Z",
    "type": "cve",
    "title": "Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy",
    "source": "EEF",
    "references": "https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2\nhttps://cna.erlef.org/cves/CVE-2026-32688.html\nhttps://osv.dev/vulnerability/EEF-CVE-2026-32688\nhttps://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b",
    "id": "CVE-2026-32688",
    "bulletinFamily": "",
    "cwe": [
        "CWE-770"
    ],
    "cvelist": null,
    "sourceData": "elixir-plug plug_cowboy 2.0.0\nelixir-plug plug_cowboy 12ecfd024bb179d48b018fecf074e43fe6a19c83",
    "sourceHref": "",
    "cvss": {
        "score": 8.7,
        "severity": "HIGH",
        "vector": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "plug_cowboy",
    "version": "2.0.0",
    "vendor": "elixir-plug",
    "ai_description": "Unauthenticated remote denial of service via atom table exhaustion in elixir-plug plug_cowboy",
    "ai_severity": "High",
    "ai_vendor": "Elixir-Plug",
    "ai_product": "plug_cowboy",
    "ai_version": "2.0.0 to 2.8.0",
    "ai_score": 8.7
}