# CVE-2026-56811: Phoenix transports do not limit channel joins per connection, enabling process-exhaustion denial of service > Unauthenticated attackers can exhaust server processes by joining unlimited channels on a single connection, causing denial of service. - **Severity:** High 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`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 7 Jul 2026 - **Updated:** 24 Sep 2026 - **Also known as:** EEF-CVE-2026-56811, GHSA-6983-jfq8-485w ## What is CVE-2026-56811? CVE-2026-56811 is a high-severity denial of service vulnerability in phoenixframework phoenix, published on 7 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### 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. Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling) ## Which versions are affected by CVE-2026-56811? 9 open source packages ship an affected version, including phoenix. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `phoenix` | Hex | From 0.11.0 | 1.5.15, 1.6.17, 1.7.24, 1.8.9 | | `phoenix` | Hex | From 0.11.0 | 1.5.15 | | `phoenix` | Hex | From 0.11.0 | 1.5.15 | | `phoenix` | Hex | From 1.6.0-rc.0 | 1.6.17 | | `phoenix` | Hex | From 1.6.0-rc.0 | 1.6.17 | | `phoenix` | Hex | From 1.7.0-rc.0 | 1.7.24 | | `phoenix` | Hex | From 1.7.0-rc.0 | 1.7.24 | | `phoenix` | Hex | From 1.8.0-rc.0 | 1.8.9 | | `phoenix` | Hex | From 1.8.0-rc.0 | 1.8.9 | Products: Phoenixframework Phoenix. ## How do I fix CVE-2026-56811? Upgrade phoenix to a fixed version for your release line: 1.5.15, 1.6.17, 1.7.24 or 1.8.9. ## Is CVE-2026-56811 being exploited? There is no known exploitation of CVE-2026-56811 in the wild and no public exploit code. ## Other vulnerabilities in phoenixframework phoenix - [CVE-2022-42975](https://insights.sbomify.com/CVE-2022-42975/): Phoenix before 1.6.14 mishandles check_origin wildcarding (high 7.5) - [CVE-2026-56812](https://insights.sbomify.com/CVE-2026-56812/): Phoenix: Presence keys colliding with `Object.prototype` members break existence checks (medium 6.3) - [CVE-2017-1000163](https://insights.sbomify.com/CVE-2017-1000163/): Phoenix Arbitrary URL Redirect (medium 6.1) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-56811 and fix it if it is affected. What it is: CVE-2026-56811 is a high-severity denial of service vulnerability in phoenixframework phoenix, published on 7 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-56811 in the wild and no public exploit code. Affected packages and fixed versions: - phoenix (Hex): affected from 0.11.0; fixed in 1.5.15, 1.6.17, 1.7.24, 1.8.9 - phoenix (Hex): affected from 0.11.0; fixed in 1.5.15 - phoenix (Hex): affected from 0.11.0; fixed in 1.5.15 - phoenix (Hex): affected from 1.6.0-rc.0; fixed in 1.6.17 - phoenix (Hex): affected from 1.6.0-rc.0; fixed in 1.6.17 - phoenix (Hex): affected from 1.7.0-rc.0; fixed in 1.7.24 - phoenix (Hex): affected from 1.7.0-rc.0; fixed in 1.7.24 - phoenix (Hex): affected from 1.8.0-rc.0; fixed in 1.8.9 - phoenix (Hex): affected from 1.8.0-rc.0; fixed in 1.8.9 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-56811/ (Markdown: https://insights.sbomify.com/CVE-2026-56811/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56811 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56811 - OSV: https://osv.dev/vulnerability/CVE-2026-56811 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-56811/ Summaries are generated and may contain mistakes; the official description above is the record.