{"id":"CVE-2026-55640","state":"PUBLISHED","title":"Nextcloud MCP Server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )","description":"Nextcloud MCP Server is a production-ready MCP server that connects AI assistants to a Nextcloud instance. Prior to 0.117.2, the POST /webhooks/nextcloud endpoint in nextcloud_mcp_server/vector/webhook_receiver.py has no authentication by default because WEBHOOK_SECRET defaults to None and startup validation does not require it. When WEBHOOK_SECRET is unset, handle_nextcloud_webhook() accepts unauthenticated requests. The payload[\"user\"][\"uid\"] field parsed in nextcloud_mcp_server/vector/webhook_parser.py is attacker-controlled and is used without an authenticated-session cross-check for Qdrant operations, allowing a network attacker to delete or trigger re-indexing of vector embeddings for any user and to destroy the semantic search index by sending forged deletion events. This issue is fixed in version 0.117.2.","publishedAt":"2026-08-25T16:03:28.085Z","updatedAt":"2026-08-25T19:20:43.689Z","severity":{"score":9.1,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["cbcoutinho nextcloud-mcp-server"],"affected":[{"vendor":"cbcoutinho","product":"nextcloud-mcp-server","versions":[{"version":"< 0.117.2","status":"affected"}]}],"references":["https://github.com/cbcoutinho/nextcloud-mcp-server/security/advisories/GHSA-8vh3-g2qg-2h2c","https://github.com/cbcoutinho/nextcloud-mcp-server/commit/4fc2b10945108cf1008ec9698291de6706ffcb73","https://github.com/cbcoutinho/nextcloud-mcp-server/tree/v0.117.2"],"weaknesses":["CWE-306"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/55xxx/CVE-2026-55640.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-55640","state":"PUBLISHED","datePublished":"2026-08-25T16:03:28.085Z","dateUpdated":"2026-08-25T19:20:43.689Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-16T23:52:12.057Z"},"containers":{"cna":{"title":"Nextcloud MCP Server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )","descriptions":[{"lang":"en","value":"Nextcloud MCP Server is a production-ready MCP server that connects AI assistants to a Nextcloud instance. Prior to 0.117.2, the POST /webhooks/nextcloud endpoint in nextcloud_mcp_server/vector/webhook_receiver.py has no authentication by default because WEBHOOK_SECRET defaults to None and startup validation does not require it. When WEBHOOK_SECRET is unset, handle_nextcloud_webhook() accepts unauthenticated requests. The payload[\"user\"][\"uid\"] field parsed in nextcloud_mcp_server/vector/webhook_parser.py is attacker-controlled and is used without an authenticated-session cross-check for Qdrant operations, allowing a network attacker to delete or trigger re-indexing of vector embeddings for any user and to destroy the semantic search index by sending forged deletion events. This issue is fixed in version 0.117.2."}],"affected":[{"vendor":"cbcoutinho","product":"nextcloud-mcp-server","versions":[{"version":"< 0.117.2","status":"affected"}]}],"references":[{"url":"https://github.com/cbcoutinho/nextcloud-mcp-server/security/advisories/GHSA-8vh3-g2qg-2h2c","name":"https://github.com/cbcoutinho/nextcloud-mcp-server/security/advisories/GHSA-8vh3-g2qg-2h2c","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/cbcoutinho/nextcloud-mcp-server/commit/4fc2b10945108cf1008ec9698291de6706ffcb73","name":"https://github.com/cbcoutinho/nextcloud-mcp-server/commit/4fc2b10945108cf1008ec9698291de6706ffcb73","tags":["x_refsource_MISC"]},{"url":"https://github.com/cbcoutinho/nextcloud-mcp-server/tree/v0.117.2","name":"https://github.com/cbcoutinho/nextcloud-mcp-server/tree/v0.117.2","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":9.1,"baseSeverity":"CRITICAL","confidentialityImpact":"NONE","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-306","lang":"en","description":"CWE-306: Missing Authentication for Critical Function","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-25T16:03:28.085Z"},"source":{"advisory":"GHSA-8vh3-g2qg-2h2c","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-25T18:38:39.313226Z","id":"CVE-2026-55640","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-25T19:20:43.689Z"}}]}}}