{
  "schema_version": "1.4.0",
  "id": "GHSA-w9fg-xffh-p362",
  "modified": "2024-09-24T20:08:23Z",
  "published": "2021-04-13T15:12:51Z",
  "aliases": [
    "CVE-2021-21394"
  ],
  "summary": "Denial of service (via resource exhaustion) due to improper input validation on third-party identifier endpoints",
  "details": "### Impact\nMissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion.\n\n### Patches\nThe issue is fixed by #9321.\n\n### Workarounds\nDepending on the needs and configuration of the homeserver a few options are available:\n\n1. Using email as third-party identifiers be disabled by not configuring the `email` setting.\n2. Using phone numbers as third-party identifiers can be disabled by ensuring that `account_threepid_delegates.msisdn` is not configured.\n3. Additionally, the affected endpoint patterns can be blocked at a reverse proxy:\n\n    * `^/_matrix/client/(r0|unstable)/register/email`\n    * `^/_matrix/client/(r0|unstable)/register/msisdn`\n    * `^/_matrix/client/(r0|unstable)/account/password`\n    * `^/_matrix/client/(r0|unstable)/account/3pid`",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H"
    },
    {
      "type": "CVSS_V4",
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "matrix-synapse"
      },
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.28.0"
            }
          ]
        }
      ]
    }
  ],
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/matrix-org/synapse/security/advisories/GHSA-w9fg-xffh-p362"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-21394"
    },
    {
      "type": "WEB",
      "url": "https://github.com/matrix-org/synapse/pull/9321"
    },
    {
      "type": "WEB",
      "url": "https://github.com/matrix-org/synapse/pull/9393"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/matrix-org/synapse"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-27.yaml"
    },
    {
      "type": "WEB",
      "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY"
    },
    {
      "type": "WEB",
      "url": "https://pypi.org/project/matrix-synapse"
    }
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "severity": "MODERATE",
    "github_reviewed": true,
    "github_reviewed_at": "2021-04-12T21:01:40Z",
    "nvd_published_at": "2021-04-12T21:15:00Z"
  }
}