GHSA-6983-jfq8-485w

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GHSA-6983-jfq8-485w

Summary: Phoenix: Unbounded channel joins per transport enables DoS over few connections

Details: ### Summary Phoenix transports do not limit the number of channels in a given connection, making it easy to spawn hundreds of thousands of processes over a single connection, and, eventually reaching the max processes VM limit. The solution is to limit the number of channels per transport, so an attacker needs to start new HTTP/WebSocket connections, allowing third-party services to apply rate limits and intervene more easily. ### Impact An unauthenticated remote attacker can cause a denial of service against any Phoenix app that exposes LongPoll/WebSocket transports.

References: https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w, https://nvd.nist.gov/vuln/detail/CVE-2026-56811, https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a, https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1, https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218, https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e, https://cna.erlef.org/cves/CVE-2026-56811.html, https://github.com/phoenixframework/phoenix, https://osv.dev/vulnerability/EEF-CVE-2026-56811