{"id":"CVE-2026-32688","state":"PUBLISHED","title":"Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy","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.","publishedAt":"2026-04-27T13:45:35.160Z","updatedAt":"2026-04-29T17:08:07.227Z","severity":{"score":8.7,"label":"High","version":"4.0","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","source":"EEF"},"assigner":"EEF","products":["elixir-plug plug_cowboy"],"affected":[{"vendor":"elixir-plug","product":"plug_cowboy","packageName":"plug_cowboy","packageURL":"pkg:hex/plug_cowboy","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","lessThan":"2.8.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Plug.Cowboy.Conn'"],"programFiles":["lib/plug/cowboy/conn.ex"],"programRoutines":[{"name":"'Elixir.Plug.Cowboy.Conn':conn/1"}],"repo":"https://github.com/elixir-plug/plug_cowboy"},{"vendor":"elixir-plug","product":"plug_cowboy","packageName":"elixir-plug/plug_cowboy","packageURL":"pkg:github/elixir-plug/plug_cowboy","defaultStatus":"unaffected","versions":[{"version":"12ecfd024bb179d48b018fecf074e43fe6a19c83","status":"affected","lessThan":"bfb34cb45eb354e56437f7023fb306de1bf9c19b","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Plug.Cowboy.Conn'"],"programFiles":["lib/plug/cowboy/conn.ex"],"programRoutines":[{"name":"'Elixir.Plug.Cowboy.Conn':conn/1"}],"repo":"https://github.com/elixir-plug/plug_cowboy"}],"references":["https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2","https://cna.erlef.org/cves/CVE-2026-32688.html","https://osv.dev/vulnerability/EEF-CVE-2026-32688","https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b"],"weaknesses":["CWE-770"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/32xxx/CVE-2026-32688.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-32688","state":"PUBLISHED","datePublished":"2026-04-27T13:45:35.160Z","dateUpdated":"2026-04-29T17:08:07.227Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-03-13T09:12:14.475Z"},"containers":{"cna":{"title":"Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy","descriptions":[{"lang":"en","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."}],"affected":[{"vendor":"elixir-plug","product":"plug_cowboy","packageName":"plug_cowboy","packageURL":"pkg:hex/plug_cowboy","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","lessThan":"2.8.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Plug.Cowboy.Conn'"],"programFiles":["lib/plug/cowboy/conn.ex"],"programRoutines":[{"name":"'Elixir.Plug.Cowboy.Conn':conn/1"}],"repo":"https://github.com/elixir-plug/plug_cowboy"},{"vendor":"elixir-plug","product":"plug_cowboy","packageName":"elixir-plug/plug_cowboy","packageURL":"pkg:github/elixir-plug/plug_cowboy","defaultStatus":"unaffected","versions":[{"version":"12ecfd024bb179d48b018fecf074e43fe6a19c83","status":"affected","lessThan":"bfb34cb45eb354e56437f7023fb306de1bf9c19b","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"],"modules":["'Elixir.Plug.Cowboy.Conn'"],"programFiles":["lib/plug/cowboy/conn.ex"],"programRoutines":[{"name":"'Elixir.Plug.Cowboy.Conn':conn/1"}],"repo":"https://github.com/elixir-plug/plug_cowboy"}],"references":[{"url":"https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-32688.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-32688","tags":["related"]},{"url":"https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b","tags":["patch"]}],"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":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-04-29T17:08:07.227Z"},"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"}],"impacts":[{"capecId":"CAPEC-125","descriptions":[{"lang":"en","value":"CAPEC-125 Flooding"}]}],"source":{"discovery":"EXTERNAL"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"Disable HTTP/2 on the <tt>Plug.Cowboy.https/3</tt> listener by passing <tt>protocol_options: %{protocols: [:http]}</tt> 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"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-04-27T19:04:33.154446Z","id":"CVE-2026-32688","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-04-27T20:11:22.651Z"}}]}}}