Vulnerability-Lookup

GHSA-8Q93-326V-3M7G

Vulnerability from github – Published: 2026-05-14 16:18 – Updated: 2026-05-14 16:18

Summary

Synapse CPU starvation (Denial of Service)

Details

Impact

Local authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service.

Homeservers that trust all their local users are not at risk.

Patches

Update to Synapse 1.152.1 or later.

Workarounds

If Synapse is deployed behind a reverse proxy, the reverse proxy could be configured to limit the rate of user requests, preventing or increasing the difficulty of the attack.

Identifiers

ELEMENTSEC-2026-1706

For more information

If you have any questions or comments about this advisory, please email us at security at element.io.

Severity

7.1 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "matrix-synapse"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.152.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-45078"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-14T16:18:40Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Impact\n\nLocal authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service.\n\nHomeservers that trust all their local users are not at risk.\n\n### Patches\n\nUpdate to Synapse 1.152.1 or later.\n\n### Workarounds\n\nIf Synapse is deployed behind a reverse proxy, the reverse proxy could be configured to limit the rate of user requests,\npreventing or increasing the difficulty of the attack.\n\n### Identifiers\n\n- ELEMENTSEC-2026-1706\n\n### For more information\n\nIf you have any questions or comments about this advisory, please email us at [security at element.io](mailto:security@element.io).",
  "id": "GHSA-8q93-326v-3m7g",
  "modified": "2026-05-14T16:18:41Z",
  "published": "2026-05-14T16:18:40Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/element-hq/synapse/security/advisories/GHSA-8q93-326v-3m7g"
    },
    {
      "type": "WEB",
      "url": "https://github.com/element-hq/synapse/issues/19394"
    },
    {
      "type": "WEB",
      "url": "https://github.com/element-hq/synapse/commit/3f58bc50dfba5768ee43ce48c5e74c25ba0b078a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/element-hq/synapse"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Synapse CPU starvation (Denial of Service)"
}

CVE-2026-45078 (GCVE-0-2026-45078)

Vulnerability from cvelistv5 – Published: 2026-05-28 15:52 – Updated: 2026-05-29 15:31

Title

Synapse CPU starvation (Denial of Service)

Summary

Synapse is an open source Matrix homeserver implementation. Prior to 1.152.1, local authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service. This vulnerability is fixed in 1.152.1.

Severity

6.8 (Medium)


                        
                          CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CWE

CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/element-hq/synapse/security/ad…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
element-hq	synapse	Affected: < 1.152.1

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-45078",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-29T15:31:35.828810Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-29T15:31:44.793Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "synapse",
          "vendor": "element-hq",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.152.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Synapse is an open source Matrix homeserver implementation. Prior to 1.152.1, local authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service. This vulnerability is fixed in 1.152.1."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "LOCAL",
            "baseScore": 6.8,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "LOW",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-770",
              "description": "CWE-770: Allocation of Resources Without Limits or Throttling",
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      "providerMetadata": {
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      },
      "references": [
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          "name": "https://github.com/element-hq/synapse/security/advisories/GHSA-8q93-326v-3m7g",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/element-hq/synapse/security/advisories/GHSA-8q93-326v-3m7g"
        }
      ],
      "source": {
        "advisory": "GHSA-8q93-326v-3m7g",
        "discovery": "UNKNOWN"
      },
      "title": "Synapse CPU starvation (Denial of Service)"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-45078",
    "datePublished": "2026-05-28T15:52:04.765Z",
    "dateReserved": "2026-05-08T18:45:10.097Z",
    "dateUpdated": "2026-05-29T15:31:44.793Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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