CVE-2026-55640: Cbcoutinho Nextcloud-Mcp-Server

Critical severity, CVSS 9.1. EPSS: 0.7% chance of exploitation in the next 30 days.

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 products

• Cbcoutinho Nextcloud-Mcp-Server: before 0.117.2 (fixed in 0.117.2)

Published 2026-08-25. Last modified 2026-09-09.