CVE-2026-56811 (GCVE-0-2026-56811)

Vulnerability from cvelistv5 – Published: 2026-07-07 15:09 – Updated: 2026-07-07 16:14
VLAI
Title
Phoenix transports do not limit channel joins per connection, enabling process-exhaustion denial of service
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 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
8.7 (High)
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
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
EEF
References
Impacted products
Vendor Product Version
phoenixframework phoenix Affected: 0.11.0 , < 1.5.15 (semver)
Affected: 1.6.0-rc.0 , < 1.6.17 (semver)
Affected: 1.7.0-rc.0 , < 1.7.24 (semver)
Affected: 1.8.0-rc.0 , < 1.8.9 (semver)
    cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*
 Create a notification for this product.
phoenixframework phoenix Affected: 14a297e88023cb280a577962a49a0bbdeef9f4eb , < * (git)
    cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Peter Ullrich Steffen Deusch Jonatan Männchen José Valim
Show details on NVD website
To clipboard 

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    "vulnrichment": {
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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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eAllocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (\u003ctt\u003ePhoenix.Socket\u003c/tt\u003e 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).\u003c/p\u003e\u003cp\u003eThis vulnerability is associated with program files \u003ctt\u003elib/phoenix/socket.ex\u003c/tt\u003e and program routine \u003ctt\u003e\u0027Elixir.Phoenix.Socket\u0027:handle_in/4\u003c/tt\u003e.\u003c/p\u003e\u003cp\u003ePhoenix transports do not limit the number of channels that a single transport process may join. Every \u003ctt\u003ephx_join\u003c/tt\u003e 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 \u003ctt\u003ephx_join\u003c/tt\u003e 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. 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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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eThe 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 \u003ctt\u003ephx_join\u003c/tt\u003e 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.\u003c/p\u003e\", \"base64\": false}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.5.15\", \"versionStartIncluding\": \"0.11.0\"}, {\"criteria\": \"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.6.17\", \"versionStartIncluding\": \"1.6.0-rc.0\"}, {\"criteria\": \"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.7.24\", \"versionStartIncluding\": \"1.7.0-rc.0\"}, {\"criteria\": \"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.8.9\", \"versionStartIncluding\": \"1.8.0-rc.0\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-07-07T16:14:39.702Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-56811\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-07T16:14:39.702Z\", \"dateReserved\": \"2026-06-23T12:29:02.507Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-07-07T15:09:57.581Z\", \"assignerShortName\": \"EEF\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.