{"id":"CVE-2026-56811","aliases":["EEF-CVE-2026-56811","EUVD-2026-42049","GHSA-6983-jfq8-485w"],"status":"published","title":"Phoenix transports do not limit channel joins per connection, enabling process-exhaustion denial of service","description":"Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll).\n\nThis vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4.\n\nPhoenix transports do not limit the number of channels that a single transport process may join. Every phx_join message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of phx_join messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it.\n\nThe fix adds a :max_channels_per_transport option (default 100) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them.\n\nThis issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.","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":"2026-11-12","score":0.00775,"percentile":0.56259,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-770"],"published":"2026-07-07T15:09:57Z","modified":"2026-10-28T02:30:23Z","fixes":[{"ecosystem":"Hex","package":"phoenix","fixed_in":["1.5.15","1.6.17","1.7.24","1.8.9"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.11.0"},{"fixed":"1.5.15"}]}]},{"source":"ghsa","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.6.0-rc.0"},{"fixed":"1.6.17"}]}]},{"source":"ghsa","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.7.0-rc.0"},{"fixed":"1.7.24"}]}]},{"source":"ghsa","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.8.0-rc.0"},{"fixed":"1.8.9"}]}]},{"source":"osv","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"SEMVER","events":[{"introduced":"0.11.0"},{"fixed":"1.5.15"}]},{"type":"SEMVER","events":[{"introduced":"1.6.0-rc.0"},{"fixed":"1.6.17"}]},{"type":"SEMVER","events":[{"introduced":"1.7.0-rc.0"},{"fixed":"1.7.24"}]},{"type":"SEMVER","events":[{"introduced":"1.8.0-rc.0"},{"fixed":"1.8.9"}]}],"versions":["0.11.0","0.12.0","0.13.0","0.13.1","0.14.0","0.15.0","0.16.0","0.16.1","0.17.0","0.17.1","1.0.0","1.0.1","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.1.5","1.1.6","1.1.7","1.1.8","1.1.9","1.2.0","1.2.0-rc.0","1.2.0-rc.1","1.2.1","1.2.2","1.2.3","1.2.4","1.2.5","1.3.0","1.3.0-rc.0","1.3.0-rc.1","1.3.0-rc.2","1.3.0-rc.3","1.3.1","1.3.2","1.3.3","1.3.4","1.3.5","1.4.0","1.4.0-rc.0","1.4.0-rc.1","1.4.0-rc.2","1.4.0-rc.3","1.4.1","1.4.10","1.4.11","1.4.12","1.4.13","1.4.14","1.4.15","1.4.16","1.4.17","1.4.18","1.4.2","1.4.3","1.4.4","1.4.5","1.4.6","1.4.7","1.4.8","1.4.9","1.5.0","1.5.0-rc.0","1.5.1","1.5.10","1.5.11","1.5.12","1.5.13","1.5.14","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.5.8","1.5.9","1.6.0","1.6.0-rc.0","1.6.0-rc.1","1.6.1","1.6.10","1.6.11","1.6.12","1.6.13","1.6.14","1.6.15","1.6.16","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","1.7.0","1.7.0-rc.0","1.7.0-rc.1","1.7.0-rc.2","1.7.0-rc.3","1.7.1","1.7.10","1.7.11","1.7.12","1.7.13","1.7.14","1.7.15","1.7.16","1.7.17","1.7.18","1.7.19","1.7.2","1.7.20","1.7.21","1.7.22","1.7.23","1.7.3","1.7.4","1.7.5","1.7.6","1.7.7","1.7.8","1.7.9","1.8.0","1.8.0-rc.0","1.8.0-rc.1","1.8.0-rc.2","1.8.0-rc.3","1.8.0-rc.4","1.8.1","1.8.2","1.8.3","1.8.4","1.8.5","1.8.6","1.8.7","1.8.8"]},{"source":"osv","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"SEMVER","events":[{"introduced":"0.11.0"},{"fixed":"1.5.15"}]}],"versions":["0.11.0","0.12.0","0.13.0","0.13.1","0.14.0","0.15.0","0.16.0","0.16.1","0.17.0","0.17.1","1.0.0","1.0.1","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.1.5","1.1.6","1.1.7","1.1.8","1.1.9","1.2.0","1.2.0-rc.0","1.2.0-rc.1","1.2.1","1.2.2","1.2.3","1.2.4","1.2.5","1.3.0","1.3.0-rc.0","1.3.0-rc.1","1.3.0-rc.2","1.3.0-rc.3","1.3.1","1.3.2","1.3.3","1.3.4","1.3.5","1.4.0","1.4.0-rc.0","1.4.0-rc.1","1.4.0-rc.2","1.4.0-rc.3","1.4.1","1.4.10","1.4.11","1.4.12","1.4.13","1.4.14","1.4.15","1.4.16","1.4.17","1.4.18","1.4.2","1.4.3","1.4.4","1.4.5","1.4.6","1.4.7","1.4.8","1.4.9","1.5.0","1.5.0-rc.0","1.5.1","1.5.10","1.5.11","1.5.12","1.5.13","1.5.14","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.5.8","1.5.9"]},{"source":"osv","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"SEMVER","events":[{"introduced":"1.6.0-rc.0"},{"fixed":"1.6.17"}]}],"versions":["1.6.0","1.6.0-rc.0","1.6.0-rc.1","1.6.1","1.6.10","1.6.11","1.6.12","1.6.13","1.6.14","1.6.15","1.6.16","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9"]},{"source":"osv","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"SEMVER","events":[{"introduced":"1.7.0-rc.0"},{"fixed":"1.7.24"}]}],"versions":["1.7.0","1.7.0-rc.0","1.7.0-rc.1","1.7.0-rc.2","1.7.0-rc.3","1.7.1","1.7.10","1.7.11","1.7.12","1.7.13","1.7.14","1.7.15","1.7.16","1.7.17","1.7.18","1.7.19","1.7.2","1.7.20","1.7.21","1.7.22","1.7.23","1.7.3","1.7.4","1.7.5","1.7.6","1.7.7","1.7.8","1.7.9"]},{"source":"osv","ecosystem":"Hex","package":"phoenix","ranges":[{"type":"SEMVER","events":[{"introduced":"1.8.0-rc.0"},{"fixed":"1.8.9"}]}],"versions":["1.8.0","1.8.0-rc.0","1.8.0-rc.1","1.8.0-rc.2","1.8.0-rc.3","1.8.0-rc.4","1.8.1","1.8.2","1.8.3","1.8.4","1.8.5","1.8.6","1.8.7","1.8.8"]}],"products":[{"vendor":"phoenixframework","product":"phoenix"}],"references":[{"url":"https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w","tags":["vendor-advisory","related","Patch","Vendor Advisory","advisory","web"]},{"url":"https://cna.erlef.org/cves/CVE-2026-56811.html","tags":["related","Mitigation","Patch","Third Party Advisory","web"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-56811","tags":["related","Mitigation","Third Party Advisory","web"]},{"url":"https://github.com/phoenixframework/phoenix/commit/14a297e88023cb280a577962a49a0bbdeef9f4eb","tags":["related","fix","web"]},{"url":"https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218","tags":["patch","Patch","fix","web"]},{"url":"https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e","tags":["patch","Patch","fix","web"]},{"url":"https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1","tags":["patch","Patch","fix","web"]},{"url":"https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a","tags":["patch","Patch","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-56811","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-6983-jfq8-485w"},{"url":"https://github.com","tags":["web"]},{"url":"https://repo.hex.pm","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/56xxx/CVE-2026-56811.json","tags":["advisory"]},{"url":"https://github.com/phoenixframework/phoenix","tags":["package"]},{"url":"https://hex.pm/packages/phoenix","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-56811","title":"Phoenix transports do not limit channel joins per connection, enabling process-exhaustion denial of service","description":"Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll).\n\nThis vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4.\n\nPhoenix transports do not limit the number of channels that a single transport process may join. Every phx_join message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of phx_join messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it.\n\nThe fix adds a :max_channels_per_transport option (default 100) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them.\n\nThis issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.","status":"published","published":"2026-07-07T15:09:57.581Z","modified":"2026-09-24T21:28:45.227Z","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":"2026-11-02T13:37:02.780526Z"}],"euvd":[{"id":"EUVD-2026-42049","description":"Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll).\n\nThis vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4.\n\nPhoenix transports do not limit the number of channels that a single transport process may join. Every phx_join message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of phx_join messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it.\n\nThe fix adds a :max_channels_per_transport option (default 100) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them.\n\nThis issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.","status":"published","published":"2026-07-07T15:09:57Z","modified":"2026-09-24T21:28:45Z","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":"2026-11-02T17:27:56.296478Z"}],"ghsa":[{"id":"GHSA-6983-jfq8-485w","title":"Phoenix: Unbounded channel joins per transport enables DoS over few connections","description":"### Summary\n\nPhoenix transports do not limit the number of channels in a given connection, making it easy to spawn hundreds of thousands of processes over a single connection, and, eventually reaching the max processes VM limit. The solution is to limit the number of channels per transport, so an attacker needs to start new HTTP/WebSocket connections, allowing third-party services to apply rate limits and intervene more easily.\n\n### Impact\n\nAn unauthenticated remote attacker can cause a denial of service against any Phoenix app that exposes LongPoll/WebSocket transports.","status":"published","published":"2026-09-03T20:33:03Z","modified":"2026-09-03T20:33:04Z","cvss":[{"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"},{"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":"2026-11-02T14:41:11.621873Z"}],"nvd":[{"id":"CVE-2026-56811","description":"Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll).\n\nThis vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4.\n\nPhoenix transports do not limit the number of channels that a single transport process may join. Every phx_join message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of phx_join messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it.\n\nThe fix adds a :max_channels_per_transport option (default 100) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them.\n\nThis issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.","status":"published","published":"2026-07-07T16:16:40.71Z","modified":"2026-10-25T20:10:00.147Z","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":"2026-11-02T14:12:28.040501Z"}],"osv":[{"id":"CVE-2026-56811","title":"Phoenix transports do not limit channel joins per connection, enabling process-exhaustion denial of service","description":"Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll).\n\nThis vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4.\n\nPhoenix transports do not limit the number of channels that a single transport process may join. Every phx_join message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of phx_join messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it.\n\nThe fix adds a :max_channels_per_transport option (default 100) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them.\n\nThis issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.","status":"published","published":"2026-07-07T15:09:57.581Z","modified":"2026-10-28T02:30:23.042129668Z","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":"2026-11-02T15:45:12.016252Z"},{"id":"EEF-CVE-2026-56811","title":"Phoenix transports do not limit channel joins per connection, enabling process-exhaustion denial of service","description":"## Summary\n\nAllocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (`Phoenix.Socket` module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll).\n\nThis vulnerability is associated with program files `lib/phoenix/socket.ex` and program routine `'Elixir.Phoenix.Socket':handle_in/4`.\n\nPhoenix transports do not limit the number of channels that a single transport process may join. Every `phx_join` message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of `phx_join` messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it.\n\nThe fix adds a `:max_channels_per_transport` option (default `100`) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them.\n\nThis issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.\n\n## Workarounds\n\nFront the socket endpoint with a reverse proxy that limits the number and rate of channel-join frames per connection, or disable transports that are not needed (for example remove `longpoll: true` from the `socket` declaration where the LongPoll transport is not required). Lowering the BEAM `+P` maximum process limit does not prevent the exhaustion and can make it easier to trigger.\n\n## Configurations\n\nThe application must mount a Phoenix socket that defines channels and expose it over HTTP so that a client can reach a channel transport (WebSocket or LongPoll) and send `phx_join` messages. The WebSocket transport is enabled by default on a mounted socket, while the LongPoll transport is opt-in. Applications that do not mount a socket with channels are not affected.","status":"published","published":"2026-07-07T15:09:57.581Z","modified":"2026-09-24T21:30:06.583902961Z","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":"2026-11-02T15:46:33.520522Z"},{"id":"GHSA-6983-jfq8-485w","title":"Phoenix: Unbounded channel joins per transport enables DoS over few connections","description":"### Summary\n\nPhoenix transports do not limit the number of channels in a given connection, making it easy to spawn hundreds of thousands of processes over a single connection, and, eventually reaching the max processes VM limit. The solution is to limit the number of channels per transport, so an attacker needs to start new HTTP/WebSocket connections, allowing third-party services to apply rate limits and intervene more easily.\n\n### Impact\n\nAn unauthenticated remote attacker can cause a denial of service against any Phoenix app that exposes LongPoll/WebSocket transports.","status":"published","published":"2026-09-03T20:33:03Z","modified":"2026-09-03T20:45:04.969699139Z","cvss":[{"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"},{"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":"2026-11-02T15:46:39.618611Z"}]}}