{"id":"CVE-2026-32688","aliases":["EEF-CVE-2026-32688","EUVD-2026-25845","GHSA-q8x4-x7mp-5vg2"],"status":"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.","severity":{"version":"4.0","score":8.7,"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","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00545,"percentile":0.46212,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-770"],"published":"2026-04-27T13:45:35Z","modified":"2026-10-28T02:30:39Z","fixes":[{"ecosystem":"Hex","package":"plug_cowboy","fixed_in":["2.8.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Hex","package":"plug_cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0"},{"fixed":"2.8.1"}]}]},{"source":"osv","ecosystem":"Hex","package":"plug_cowboy","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"2.8.1"}]}],"versions":["2.0.0","2.0.1","2.0.2","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.3.0","2.4.0","2.4.1","2.5.0","2.5.1","2.5.2","2.6.0","2.6.1","2.6.2","2.7.0","2.7.1","2.7.2","2.7.3","2.7.4","2.7.5","2.8.0"]},{"source":"osv","ecosystem":"Hex","package":"plug_cowboy","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"2.8.1"}]}],"versions":["2.0.0","2.0.1","2.0.2","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.3.0","2.4.0","2.4.1","2.5.0","2.5.1","2.5.2","2.6.0","2.6.1","2.6.2","2.7.0","2.7.1","2.7.2","2.7.3","2.7.4","2.7.5","2.8.0"]}],"products":[{"vendor":"elixir-plug","product":"plug.cowboy"},{"vendor":"elixir-plug","product":"plug_cowboy"}],"references":[{"url":"https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2","tags":["vendor-advisory","related","Vendor Advisory","advisory","web"]},{"url":"https://cna.erlef.org/cves/CVE-2026-32688.html","tags":["related","Third Party Advisory","web"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-32688","tags":["related","Third Party Advisory","web"]},{"url":"https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b","tags":["patch","Patch","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-32688","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-q8x4-x7mp-5vg2"},{"url":"https://github.com","tags":["web"]},{"url":"https://repo.hex.pm","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32688.json","tags":["advisory"]},{"url":"https://github.com/elixir-plug/plug_cowboy","tags":["package"]},{"url":"https://hex.pm/packages/plug_cowboy","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-32688","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.","status":"published","published":"2026-04-27T13:45:35.16Z","modified":"2026-04-29T17:08:07.227Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high","assessor":"cna"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:19:57.100857Z"}],"euvd":[{"id":"EUVD-2026-25845","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.","status":"published","published":"2026-04-27T13:45:35Z","modified":"2026-04-29T17:08:07Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high"}],"updated_at":"2026-11-02T19:05:19.555165Z"}],"ghsa":[{"id":"GHSA-q8x4-x7mp-5vg2","title":"Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 `:scheme` atom-table exhaustion","description":"## Summary\n\nAn unauthenticated remote denial-of-service vulnerability in `Plug.Cowboy.Conn` allows any attacker who can reach an HTTPS Plug.Cowboy listener via HTTP/2 to permanently exhaust the BEAM atom table and crash the entire Erlang VM.\n\n## Am I Affected?\n\nAll users running plug_cowboy with HTTP/2 may be affected, this includes Phoenix applications. If another HTTP adapter such as Bandit is used, then the consuming project is not affected. If the HTTP/2 endpoint is exposed directly (without a proxy) then the project will be affected. If a proxy is in use then it depends on the proxy configuration. Many proxies use HTTP/1.1 internally, and would be unaffected.\n\n## Impact\n\nThe vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.\n\n## Mitigation\n\nUsers are advised to update to plug_cowboy v2.8.1 to mitigate this issue.\n\n## Credits\nPlug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.","status":"published","published":"2026-05-05T21:46:09Z","modified":"2026-05-05T21:46:10Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:40:01.917039Z"}],"nvd":[{"id":"CVE-2026-32688","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.","status":"published","published":"2026-04-27T14:16:47.34Z","modified":"2026-10-26T21:10:00.17Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:12:16.252509Z"}],"osv":[{"id":"CVE-2026-32688","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.","status":"published","published":"2026-04-27T13:45:35.16Z","modified":"2026-10-28T02:30:39.889518345Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:45:01.548715Z"},{"id":"EEF-CVE-2026-32688","title":"Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy","description":"## Summary\n\nAllocation 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.\n\n## Workarounds\n\nDisable 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.","status":"published","published":"2026-04-27T13:45:35.16Z","modified":"2026-09-08T03:45:09.913451925Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:33.047032Z"},{"id":"GHSA-q8x4-x7mp-5vg2","title":"Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 `:scheme` atom-table exhaustion","description":"## Summary\n\nAn unauthenticated remote denial-of-service vulnerability in `Plug.Cowboy.Conn` allows any attacker who can reach an HTTPS Plug.Cowboy listener via HTTP/2 to permanently exhaust the BEAM atom table and crash the entire Erlang VM.\n\n## Am I Affected?\n\nAll users running plug_cowboy with HTTP/2 may be affected, this includes Phoenix applications. If another HTTP adapter such as Bandit is used, then the consuming project is not affected. If the HTTP/2 endpoint is exposed directly (without a proxy) then the project will be affected. If a proxy is in use then it depends on the proxy configuration. Many proxies use HTTP/1.1 internally, and would be unaffected.\n\n## Impact\n\nThe vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.\n\n## Mitigation\n\nUsers are advised to update to plug_cowboy v2.8.1 to mitigate this issue.\n\n## Credits\nPlug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.","status":"published","published":"2026-05-05T21:46:09Z","modified":"2026-05-05T22:14:10.498322Z","cvss":[{"version":"4.0","score":8.7,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:54.40888Z"}]}}