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CVE-2026-55640— Nextcloud MCP Server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )

Quick assessment

Affected
cbcoutinho nextcloud-mcp-server
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Nextcloud MCP Server 是一款面向生产环境的 MCP（Model Context Protocol）服务器，用于将 AI 助手连接到 Nextcloud 实例。在版本 0.117.2 之前，nextcloud_mcp_server/vector/webhook_receiver.py 中的 POST /webhooks/nextcloud 接口默认缺乏身份验证，因为 WEBHOOK_SECRET 的默认值为 None，且启动时的验证逻辑并不强制要求设置该参数。当未设置 WEBHOOK_SECRET

CVSS 9.1 · Critical

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
cbcoutinho nextcloud-mcp-server < 0.117.2 affected
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I. Basic Information for CVE-2026-55640

Vulnerability Information
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Vulnerability Title
Nextcloud MCP Server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
关键功能的认证机制缺失
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
cbcoutinho nextcloud-mcp-server < 0.117.2 -

II. Public POCs for CVE-2026-55640

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 9963 chars
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III. Intelligence Information for CVE-2026-55640

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Vendor Advisories for CVE-2026-55640 (1)

Other References for CVE-2026-55640 (1)

IV. Related Vulnerabilities

Same weakness: CWE-306

V. Comments for CVE-2026-55640

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