Search criteria ⓘ Use this form to refine search results.
Full-text search supports keyword queries with ranking and filtering.
You can combine vendor, product, and sources to narrow results.
Enable “Apply ordering” to sort by date instead of relevance.

1 vulnerability by elixir-plug

CVE-2026-32688 (GCVE-0-2026-32688)

Vulnerability from cvelistv5 – Published: 2026-04-27 13:45 – Updated: 2026-04-29 17:08
VLAI?
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.
Severity ?
8.7 (High)
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
CWE
  • CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
EEF
References
Impacted products
Vendor Product Version
elixir-plug plug_cowboy Affected: 2.0.0 , < 2.8.1 (semver)
    cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*
 Create a notification for this product.
    elixir-plug plug_cowboy Affected: 12ecfd024bb179d48b018fecf074e43fe6a19c83 , < bfb34cb45eb354e56437f7023fb306de1bf9c19b (git)
    cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Peter Ullrich
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-32688",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-04-27T19:04:33.154446Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-04-27T20:11:22.651Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://repo.hex.pm",
          "cpes": [
            "cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Plug.Cowboy.Conn\u0027"
          ],
          "packageName": "plug_cowboy",
          "packageURL": "pkg:hex/plug_cowboy",
          "product": "plug_cowboy",
          "programFiles": [
            "lib/plug/cowboy/conn.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Plug.Cowboy.Conn\u0027:conn/1"
            }
          ],
          "repo": "https://github.com/elixir-plug/plug_cowboy",
          "vendor": "elixir-plug",
          "versions": [
            {
              "lessThan": "2.8.1",
              "status": "affected",
              "version": "2.0.0",
              "versionType": "semver"
            }
          ]
        },
        {
          "collectionURL": "https://github.com",
          "cpes": [
            "cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Plug.Cowboy.Conn\u0027"
          ],
          "packageName": "elixir-plug/plug_cowboy",
          "packageURL": "pkg:github/elixir-plug/plug_cowboy",
          "product": "plug_cowboy",
          "programFiles": [
            "lib/plug/cowboy/conn.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Plug.Cowboy.Conn\u0027:conn/1"
            }
          ],
          "repo": "https://github.com/elixir-plug/plug_cowboy",
          "vendor": "elixir-plug",
          "versions": [
            {
              "lessThan": "bfb34cb45eb354e56437f7023fb306de1bf9c19b",
              "status": "affected",
              "version": "12ecfd024bb179d48b018fecf074e43fe6a19c83",
              "versionType": "git"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "2.8.1",
                  "versionStartIncluding": "2.0.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ],
          "operator": "AND"
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Peter Ullrich"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion.\u003cp\u003e\u003ctt\u003ePlug.Cowboy.Conn.conn/1\u003c/tt\u003e in \u003ctt\u003elib/plug/cowboy/conn.ex\u003c/tt\u003e calls \u003ctt\u003eString.to_atom/1\u003c/tt\u003e on the value returned by \u003ctt\u003e:cowboy_req.scheme/1\u003c/tt\u003e. For HTTP/2 connections, cowlib passes the client-supplied \u003ctt\u003e:scheme\u003c/tt\u003e 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 \u003ctt\u003e:scheme\u003c/tt\u003e values, causing the Erlang VM to abort with \u003ctt\u003esystem_limit\u003c/tt\u003e and taking down the entire node.\u003c/p\u003e\u003cp\u003eThis vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header.\u003c/p\u003e\u003cp\u003eThis issue affects plug_cowboy: from 2.0.0 before 2.8.1.\u003c/p\u003e"
            }
          ],
          "value": "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."
        }
      ],
      "impacts": [
        {
          "capecId": "CAPEC-125",
          "descriptions": [
            {
              "lang": "en",
              "value": "CAPEC-125 Flooding"
            }
          ]
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 8.7,
            "baseSeverity": "HIGH",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "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",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-770",
              "description": "CWE-770 Allocation of Resources Without Limits or Throttling",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-29T17:08:07.227Z",
        "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "shortName": "EEF"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory",
            "related"
          ],
          "url": "https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2"
        },
        {
          "tags": [
            "related"
          ],
          "url": "https://cna.erlef.org/cves/CVE-2026-32688.html"
        },
        {
          "tags": [
            "related"
          ],
          "url": "https://osv.dev/vulnerability/EEF-CVE-2026-32688"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy",
      "workarounds": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "Disable HTTP/2 on the \u003ctt\u003ePlug.Cowboy.https/3\u003c/tt\u003e listener by passing \u003ctt\u003eprotocol_options: %{protocols: [:http]}\u003c/tt\u003e in the cowboy options. This restricts the listener to HTTP/1.1, where the scheme is derived from the listener type and is not attacker-controlled."
            }
          ],
          "value": "Disable HTTP/2 on the Plug.Cowboy.https/3 listener by passing protocol_options: %{protocols: [:http]} in the cowboy options. This restricts the listener to HTTP/1.1, where the scheme is derived from the listener type and is not attacker-controlled."
        }
      ],
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
    "assignerShortName": "EEF",
    "cveId": "CVE-2026-32688",
    "datePublished": "2026-04-27T13:45:35.160Z",
    "dateReserved": "2026-03-13T09:12:14.475Z",
    "dateUpdated": "2026-04-29T17:08:07.227Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}