Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy

{
  "id": "7a09b3d22556fcf58e3404cf46ef01d426132aa66ab88accd480ac7a5747ea73",
  "url": "https://osv.dev/vulnerability/CVE-2026-32688",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy",
    "summary": "Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion. Plug.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. This vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header. This issue affects plug_cowboy: from 2.0.0 before 2.8.1.",
    "evidence": "osv:CVE-2026-32688",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-32688",
      "aliases": [
        "CVE-2026-32688",
        "EEF-CVE-2026-32688",
        "GHSA-q8x4-x7mp-5vg2"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/elixir-plug/plug_cowboy",
              "type": "GIT",
              "events": [
                {
                  "introduced": "8d60f2912743834b48544e6fd1f01f832d660cb1"
                },
                {
                  "fixed": "fd0841f4ef974b95a5050a2b5959585c56fb3776"
                },
                {
                  "fixed": "bfb34cb45eb354e56437f7023fb306de1bf9c19b"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:elixir-plug:plug.cowboy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "2.0.0"
                      },
                      {
                        "fixed": "2.8.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "bfb34cb45eb354e56437f7023fb306de1bf9c19b"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v2.8.0",
            "v2.7.5",
            "v2.7.4",
            "v2.7.3",
            "v2.7.2",
            "v2.7.1",
            "v2.7.0",
            "v2.6.2",
            "v2.6.1",
            "v2.6.0",
            "v2.5.2",
            "v2.5.1",
            "v2.5.0",
            "v2.4.0",
            "v2.3.0",
            "v2.2.2",
            "v2.2.1",
            "v2.2.0",
            "v2.1.2",
            "v2.1.1",
            "v2.1.0",
            "v2.0.2",
            "v2.0.1",
            "v2.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-32688.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:39.889518345Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-32688.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-32688",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32688.json",
        "https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-32688",
        "https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b",
        "https://github.com/elixir-plug/plug_cowboy"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32688.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-32688",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 507467,
  "published_at": "2026-04-27T13:45:35.16+00:00"
}