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.

CVE-2026-55640 affects the Nextcloud MCP Server, a production-ready server connecting AI assistants to Nextcloud instances. Prior to version 0.117.2, the POST /webhooks/nextcloud endpoint had no authentication by default because the WEBHOOK_SECRET environment variable defaulted to None and startup validation did not enforce its presence. When WEBHOOK_SECRET is unset, the handle_nextcloud_webhook() function accepts unauthenticated requests from any network attacker. The attacker-controlled payload field payload['user']['uid'] is parsed without an authenticated-session cross-check before being used in Qdrant vector database operations. This allows a remote unauthenticated 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. The vulnerability is fixed in version 0.117.2.