Vulnerability advisory

GHSA-6983-jfq8-485w

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

Published Sep 3, 2026Updated Sep 3, 2026OSV record ↗

Also known as CVE-2026-56811EEF-CVE-2026-56811

Severity

CVSS 3.xCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 4.0CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Affected versions

phoenix Hex

All phoenix advisories →

Affected	Fixed in
`0.11.0` to before 1.5.15	`1.5.15`Advisories →
Also listed as affected (84) `0.11.0` `0.12.0` `0.13.0` `0.13.1` `0.14.0` `0.15.0` `0.16.0` `0.16.1` `0.17.0` `0.17.1` `1.0.0` `1.0.1` `1.0.2` `1.0.3` `1.0.4` `1.0.5` `1.0.6` `1.1.0` `1.1.1` `1.1.2` `1.1.3` `1.1.4` `1.1.5` `1.1.6` `1.1.7` `1.1.8` `1.1.9` `1.2.0` `1.2.0-rc.0` `1.2.0-rc.1` `1.2.1` `1.2.2` `1.2.3` `1.2.4` `1.2.5` `1.3.0` `1.3.0-rc.0` `1.3.0-rc.1` `1.3.0-rc.2` `1.3.0-rc.3` `1.3.1` `1.3.2` `1.3.3` `1.3.4` `1.3.5` `1.4.0` `1.4.0-rc.0` `1.4.0-rc.1` `1.4.0-rc.2` `1.4.0-rc.3` `1.4.1` `1.4.10` `1.4.11` `1.4.12` `1.4.13` `1.4.14` `1.4.15` `1.4.16` `1.4.17` `1.4.18` `1.4.2` `1.4.3` `1.4.4` `1.4.5` `1.4.6` `1.4.7` `1.4.8` `1.4.9` `1.5.0` `1.5.0-rc.0` `1.5.1` `1.5.10` `1.5.11` `1.5.12` `1.5.13` `1.5.14` `1.5.2` `1.5.3` `1.5.4` `1.5.5` `1.5.6` `1.5.7` `1.5.8` `1.5.9`
`1.6.0-rc.0` to before 1.6.17	`1.6.17`Advisories →
Also listed as affected (19) `1.6.0` `1.6.0-rc.0` `1.6.0-rc.1` `1.6.1` `1.6.10` `1.6.11` `1.6.12` `1.6.13` `1.6.14` `1.6.15` `1.6.16` `1.6.2` `1.6.3` `1.6.4` `1.6.5` `1.6.6` `1.6.7` `1.6.8` `1.6.9`
`1.7.0-rc.0` to before 1.7.24	`1.7.24`Advisories →
Also listed as affected (28) `1.7.0` `1.7.0-rc.0` `1.7.0-rc.1` `1.7.0-rc.2` `1.7.0-rc.3` `1.7.1` `1.7.10` `1.7.11` `1.7.12` `1.7.13` `1.7.14` `1.7.15` `1.7.16` `1.7.17` `1.7.18` `1.7.19` `1.7.2` `1.7.20` `1.7.21` `1.7.22` `1.7.23` `1.7.3` `1.7.4` `1.7.5` `1.7.6` `1.7.7` `1.7.8` `1.7.9`
`1.8.0-rc.0` to before 1.8.9	`1.8.9`Advisories →
Also listed as affected (14) `1.8.0` `1.8.0-rc.0` `1.8.0-rc.1` `1.8.0-rc.2` `1.8.0-rc.3` `1.8.0-rc.4` `1.8.1` `1.8.2` `1.8.3` `1.8.4` `1.8.5` `1.8.6` `1.8.7` `1.8.8`

Description

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.