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

### 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. Source Code Location: https://github.com/phoenixframework/phoenix Affected Packages: - erlang:phoenix, affected >= 0.11.0, < 1.5.15, patched in 1.5.15 - erlang:phoenix, affected >= 1.6.0-rc.0, < 1.6.17, patched in 1.6.17 - erlang:phoenix, affected >= 1.7.0-rc.0, < 1.7.24, patched in 1.7.24 - erlang:phoenix, affected >= 1.8.0-rc.0, < 1.8.9, patched in 1.8.9 CWEs: - CWE-770: Allocation of Resources Without Limits or Throttling CVSS: - Primary: score 7.5, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS_V4: score 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 - CVSS_V3: score 7.5, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 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://osv.dev/vulnerability/EEF-CVE-2026-56811 - https://github.com/advisories/GHSA-6983-jfq8-485w