{"api_version":"1","generated_at":"2026-05-12T01:55:18+00:00","cve":"CVE-2026-32688","urls":{"html":"https://cve.report/CVE-2026-32688","api":"https://cve.report/api/cve/CVE-2026-32688.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-32688","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-32688"},"summary":{"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.","state":"PUBLISHED","assigner":"EEF","published_at":"2026-04-27 14:16:47","updated_at":"2026-04-27 18:57:20"},"problem_types":["CWE-770","CWE-770 CWE-770 Allocation of Resources Without Limits or Throttling"],"metrics":[{"version":"4.0","source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","type":"Secondary","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","data":{"version":"4.0","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","baseScore":8.7,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}},{"version":"4.0","source":"CNA","type":"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","data":{"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"}}],"references":[{"url":"https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2","name":"https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2","refsource":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://cna.erlef.org/cves/CVE-2026-32688.html","name":"https://cna.erlef.org/cves/CVE-2026-32688.html","refsource":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-32688","name":"https://osv.dev/vulnerability/EEF-CVE-2026-32688","refsource":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b","name":"https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b","refsource":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-32688","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-32688","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"elixir-plug","product":"plug_cowboy","version":"affected 2.0.0 2.8.1 semver","platforms":[]},{"source":"CNA","vendor":"elixir-plug","product":"plug_cowboy","version":"affected 12ecfd024bb179d48b018fecf074e43fe6a19c83 bfb34cb45eb354e56437f7023fb306de1bf9c19b git","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[{"source":"CNA","title":"","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.","time":"","lang":"en"}],"exploits":[],"credits":[{"source":"CNA","value":"Peter Ullrich","lang":"en"}],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"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"},"nvd":{"publishedDate":"2026-04-27 14:16:47","lastModifiedDate":"2026-04-27 18:57:20","problem_types":["CWE-770","CWE-770 CWE-770 Allocation of Resources Without Limits or Throttling"],"metrics":{"cvssMetricV40":[{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","type":"Secondary","cvssData":{"version":"4.0","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","baseScore":8.7,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"32688","Ordinal":"1","Title":"Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_c","CVE":"CVE-2026-32688","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"32688","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_c"}]}}}