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Vulnerability record · CVE-2026-55640 · published 25 August 2026

CVE-2026-55640: Missing authentication for critical function vulnerability

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.

9.1 CVSS 3.1 Critical EPSS 0.73% · top 47.6% CWE-306 · Missing authentication for critical function Deferred
9.1CVSS 3.1 base score
0.73%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
3References
9 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

References

LinkTags
https://github.com/cbcoutinho/nextcloud-mcp-server/commit/4fc2b10945108cf1008ec9698291de6706ffcb73
https://github.com/cbcoutinho/nextcloud-mcp-server/security/advisories/GHSA-8vh3-g2qg-2h2c
https://github.com/cbcoutinho/nextcloud-mcp-server/tree/v0.117.2

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Source: NIST National Vulnerability Database (record CVE-2026-55640), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.