{"containers":{"cna":{"affected":[{"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","modules":["'Elixir.Plug.Cowboy.Conn'"],"packageName":"plug_cowboy","packageURL":"pkg:hex/plug_cowboy","product":"plug_cowboy","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","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":["'Elixir.Plug.Cowboy.Conn'"],"packageName":"elixir-plug/plug_cowboy","packageURL":"pkg:github/elixir-plug/plug_cowboy","product":"plug_cowboy","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","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.<p><tt>Plug.Cowboy.Conn.conn/1</tt> in <tt>lib/plug/cowboy/conn.ex</tt> calls <tt>String.to_atom/1</tt> on the value returned by <tt>:cowboy_req.scheme/1</tt>. For HTTP/2 connections, cowlib passes the client-supplied <tt>:scheme</tt> 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 <tt>:scheme</tt> values, causing the Erlang VM to abort with <tt>system_limit</tt> and taking down the entire node.</p><p>This vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header.</p><p>This issue affects plug_cowboy: from 2.0.0 before 2.8.1.</p>"}],"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":{"Automatable":"YES","Recovery":"USER","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":8.7,"baseSeverity":"HIGH","exploitMaturity":"NOT_DEFINED","privilegesRequired":"NONE","providerUrgency":"RED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","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","vulnerabilityResponseEffort":"NOT_DEFINED"},"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":"2026-04-27T14:55:05.241Z","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 <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"}}},"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":"2026-04-27T14:55:05.241Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"}