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GHSA-6983-JFQ8-485W

Vulnerability from github – Published: 2026-09-03 20:33 – Updated: 2026-09-03 20:33
VLAI
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.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7 (High)
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
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "phoenix"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.11.0"
            },
            {
              "fixed": "1.5.15"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Hex",
        "name": "phoenix"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.6.0-rc.0"
            },
            {
              "fixed": "1.6.17"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Hex",
        "name": "phoenix"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.7.0-rc.0"
            },
            {
              "fixed": "1.7.24"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Hex",
        "name": "phoenix"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.8.0-rc.0"
            },
            {
              "fixed": "1.8.9"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-56811"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-03T20:33:03Z",
    "nvd_published_at": "2026-07-07T16:16:40Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nPhoenix 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.\n\n### Impact\n\nAn unauthenticated remote attacker can cause a denial of service against any Phoenix app that exposes LongPoll/WebSocket transports.",
  "id": "GHSA-6983-jfq8-485w",
  "modified": "2026-09-03T20:33:03Z",
  "published": "2026-09-03T20:33:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-56811"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-56811.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/phoenixframework/phoenix"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-56811"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Phoenix: Unbounded channel joins per transport enables DoS over few connections"
}



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