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Medium

Synapse's V2 state resolution weakness allows DoS from remote room members

Type: advisorySources: OSV

Synapse is an open-source Matrix homeserver. A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in the V2 state resolution algorithm. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service. Servers in private federations, or those that do not federate, are not affected. Server administrators should upgrade to 1.105.1 or later. Some workarounds are available. One can ban the malicious users or ACL block servers from the rooms and/or leave the room and purge the room using the admin API.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2024-31208
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 11:02 UTC · Revision 1

Source evidence

Synapse's V2 state resolution weakness allows DoS from remote room members

core-osv · Original source

Published 23 Apr 2024, 17:26 UTC

Synapse is an open-source Matrix homeserver. A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in the V2 state resolution algorithm. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service. Servers in private federations, or those that do not federate, are not affected. Server administrators should upgrade to 1.105.1 or later. Some workarounds are available. One can ban the malicious users or ACL block servers from the rooms and/or leave the room and purge the room using the admin API.

osv:CVE-2024-31208
Complete source record
{
  "id": "0bf00ba1099ef4b434717114ea1cd7af0e4473feedbbeb979d6a63dc082b7fac",
  "url": "https://osv.dev/vulnerability/CVE-2024-31208",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Synapse's V2 state resolution weakness allows DoS from remote room members",
    "summary": "Synapse is an open-source Matrix homeserver. A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in the V2 state resolution algorithm. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service. Servers in private federations, or those that do not federate, are not affected. Server administrators should upgrade to 1.105.1 or later. Some workarounds are available. One can ban the malicious users or ACL block servers from the rooms and/or leave the room and purge the room using the admin API.",
    "evidence": "osv:CVE-2024-31208",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2024-31208",
      "aliases": [
        "CVE-2024-31208",
        "GHSA-3h7q-rfh9-xm4v",
        "PYSEC-2024-50"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/element-hq/synapse",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "20c9e195197567c209edf45383e5d0cdd2ef2a5f"
                },
                {
                  "fixed": "55b0aa847a61774b6a3acdc4b177a20dc019f01a"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.105.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "55b0aa847a61774b6a3acdc4b177a20dc019f01a"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "20c9e195197567c209edf45383e5d0cdd2ef2a5f"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v1.105.1"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.105.0",
            "v1.105.0rc1",
            "v1.104.0rc1",
            "v1.103.0rc1",
            "v1.101.0rc1",
            "v1.100.0rc3",
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            "v0.17.3",
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            "v0.11.0",
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            "v0.10.0-r1",
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            "v0.9.2-r1",
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            "v0.7.1-r1",
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-31208.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:27.974583541Z",
      "provider": "osv",
      "references": [
        "https://github.com/element-hq/synapse/releases/tag/v1.105.1",
        "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/R6FCCO4ODTZ3FDS7TMW76PKOSEL2TQVB/",
        "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/RR53FNHV446CB37TP45GZ6F6HZLZCK3K/",
        "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VSF4NJJSTSQRJQ47PLYYSCFYKJBP7DET/",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/31xxx/CVE-2024-31208.json",
        "https://github.com/element-hq/synapse/security/advisories/GHSA-3h7q-rfh9-xm4v",
        "https://nvd.nist.gov/vuln/detail/CVE-2024-31208",
        "https://github.com/element-hq/synapse/commit/55b0aa847a61774b6a3acdc4b177a20dc019f01a"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/31xxx/CVE-2024-31208.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2024-31208",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 494833,
  "published_at": "2024-04-23T17:26:39.171+00:00"
}