CVE-2026-56811
HighAllocation 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…
Published Jul 7, 2026 · Updated Oct 8, 2026 · Also known as EEF-CVE-2026-56811, EUVD-2026-42049, GHSA-6983-jfq8-485w
Key Facts
Patch in the next maintenance window- CVE-2026-56811 is a high-severity vulnerability (CVSS 8.7 v4) affecting Phoenix (Phoenixframework).
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 0.8% probability of exploitation in the next 30 days.
- Fixed versions are available, including Phoenix *, Phoenix 1.5.15, Phoenix 1.6.17.
- Brandefense priority: patch in the next maintenance window, because of its high severity, although no exploitation is known.
CVSS v4
8.7
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
EPSS (30-day exploit likelihood)
0.8%
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
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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.
Affected Products
3 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| PhoenixPhoenixframework | >= 0.11.0, >= 1.8.0-rc.0 | 1.5.15 |
Patched Releases
Phoenix
*, 1.5.15, 1.6.17, 1.7.24, 1.8.9
Timeline
Publicly disclosed
Jul 7, 2026
Last updated
Oct 8, 2026
Weakness Type
- CWE-770 Allocation of Resources Without Limits or Throttling
References
- advisoryGHSA advisory
- advisoryhttps://github.com/CVEProject/cvelistV5/tree/main/cves/2026/56xxx/CVE-2026-56811.json
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2026-56811
- articlehttps://github.com
- articlehttps://repo.hex.pm
FAQ
Common Questions.
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).
Affected: Phoenix (Phoenixframework) versions >= 0.11.0, >= 1.8.0-rc.0. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including Phoenix *, Phoenix 1.5.15, Phoenix 1.6.17.
Brandefense priority: patch in the next maintenance window, because of its high severity, although no exploitation is known.
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