CyberSecBulletin
CVE-2026-56811NVD status: Modified

phoenix: Allocation of Resources Without Limits or Throttling

Published Updated By the CyberSecBulletin desk

CVE-2026-56811 is a high-severity allocation of resources without limits or throttling vulnerability in phoenix from Phoenixframework, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 1.5.15, 1.6.17, 1.7.24 as the first without the flaw, so updating phoenix to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.78% chance of exploitation within 30 days, higher than 56% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update phoenix to 1.5.15 or 1.6.17 or 1.7.24 or 1.8.9, whichever matches your release line, or a later version.
  2. Read the advisory on github.com for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
Phoenixframeworkphoenix0.11.0 up to, but not including, 1.5.15; 1.6.0-rc.0 up to, but not including, 1.6.17; 1.7.0-rc.0 up to, but not including, 1.7.24; 1.8.0-rc.0 up to, but not including, 1.8.9; 14a297e88023cb280a577962a49a0bbdeef9f4eb and later1.5.15, 1.6.17, 1.7.24, 1.8.9

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 4.08.7HighCNA
CVSS 3.17.5HighNVD

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

How developers prevent this class of flaw

  • Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
  • Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
  • For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

More Allocation of Resources Without Limits or Throttling vulnerabilities (CWE-770)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in phoenix

All phoenix vulnerabilities

Recent Allocation of Resources Without Limits or Throttling vulnerabilities

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