---
id: CVE-2026-56811
title: >-
  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…
summary: >-
  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…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-770
vendor: phoenixframework
product: phoenix
affected:
  - 'phoenix >= 1.2.0, < 1.5.15'
  - 'phoenix >= 1.6.0, < 1.6.17'
  - 'phoenix >= 1.7.0, < 1.7.24'
  - 'phoenix >= 1.8.0, < 1.8.9'
patched:
  - phoenix 1.8.9
published: '2026-07-07'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T22:17:00.407'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-56811'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-56811.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/phoenixframework/phoenix/commit/14a297e88023cb280a577962a49a0bbdeef9f4eb
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-56811'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-56811'
  - url: 'https://github.com/advisories/GHSA-6983-jfq8-485w'
tags:
  - nvd
  - cve.org
  - ghsa
  - erlang
epss: 0.00775
epssPercentile: 0.53888
aliases:
  - GHSA-6983-jfq8-485w
ecosystem: erlang
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-07-07T16:12:27.662417Z'
scores:
  nvd: 7.5
  cna: 8.7
  ghsa: 7.5
ingestedAt: '2026-09-03T21:08:46.069Z'
---

## Overview

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.

## Affected

- `phoenix >= 1.2.0, < 1.5.15`
- `phoenix >= 1.6.0, < 1.6.17`
- `phoenix >= 1.7.0, < 1.7.24`
- `phoenix >= 1.8.0, < 1.8.9`

## Remediation

Upgrade past the affected range:

- `phoenix 1.8.9`

## Package advisory (CVE-2026-56811)

Affected packages:

- `phoenix >= 0.11.0, < 1.5.15`
- `phoenix >= 1.6.0-rc.0, < 1.6.17`
- `phoenix >= 1.7.0-rc.0, < 1.7.24`
- `phoenix >= 1.8.0-rc.0, < 1.8.9`

Patched in:

- `phoenix 1.5.15`
- `phoenix 1.6.17`
- `phoenix 1.7.24`
- `phoenix 1.8.9`

Source: https://github.com/advisories/GHSA-6983-jfq8-485w