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CVE-2026-56811

Full vulnerability record from the local CVENow database.

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). This vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4. Phoenix 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. The 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. This 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
HIGH
CVSS score
8.7 (v4.0)
Vulnerability status
Modified
Source identifier
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Published
2026-07-07 16:16:40.710000
Last modified
2026-10-25 20:10:00.147000
View original CVE JSON 
{
  "id": "CVE-2026-56811",
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "published": "2026-07-07T16:16:40.710",
  "lastModified": "2026-10-25T20:10:00.147",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    },
    {
      "lang": "es",
      "value": "La vulnerabilidad de asignación de recursos sin límites ni estrangulamiento en phoenixframework phoenix (módulo Phoenix.Socket) permite a un atacante no autenticado causar una denegación de servicio contra cualquier punto final que monte un socket Phoenix con un transporte de canal accesible (WebSocket o LongPoll).\n\nEsta vulnerabilidad está asociada con los archivos de programa lib/phoenix/socket.ex y la rutina de programa ’Elixir.Phoenix.Socket’:handle_in/4.\n\nLos transportes de Phoenix no limitan el número de canales a los que puede unirse un único proceso de transporte. Cada mensaje phx_join que un cliente envía a través de una conexión inicia un proceso de canal persistente, y el proceso de socket acepta un número ilimitado de ellos. Por lo tanto, un único cliente no autenticado puede abrir una conexión WebSocket o LongPoll y transmitir un gran número de mensajes phx_join, generando cientos de miles de procesos de canal a través de esa única conexión y finalmente alcanzando el límite máximo de procesos de BEAM. Una vez que la tabla de procesos se agota, la máquina virtual ya no puede iniciar nuevos procesos, denegando el servicio al tráfico legítimo en todo el nodo. Debido a que la amplificación ocurre dentro de una única conexión, los límites de conexión de la capa de red y la limitación de velocidad no lo mitigan.\n\nLa solución añade una opción :max_channels_per_transport (por defecto 100) que limita el número de canales a los que puede unirse un único proceso de transporte, obligando a los clientes abusivos a abrir muchas conexiones en su lugar, donde los balanceadores de carga externos y los proxies inversos pueden estrangularlos.\n\nEste problema afecta a phoenix: desde 0.11.0 antes de 1.5.15, desde 1.6.0-rc.0 antes de 1.6.17, desde 1.7.0-rc.0 antes de 1.7.24, y desde 1.8.0-rc.0 antes de 1.8.9."
    }
  ],
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          "packageURL": "pkg:hex/phoenix",
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          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "valueDensity": "NOT_DEFINED",
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