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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.

Chris Coutinho Nextcloud MCP Server是Chris Coutinho个人开发者的一个为人工智能助手提供云存储文件访问能力的服务器组件。 Chris Coutinho Nextcloud MCP Server 0.117.2之前版本存在授权问题漏洞，该漏洞源于WEBHOOK_SECRET默认设置为None且启动验证未要求认证，导致POST /webhooks/nextcloud端点接受未认证请求，且未对payload中的user uid字段进行认证会话交叉检查，可能导致网络攻

CVSS 9.1 · Critical EPSS 0.73% · P54

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
Vulnerability Title
Chris Coutinho Nextcloud MCP Server 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Chris Coutinho Nextcloud MCP Server是Chris Coutinho个人开发者的一个为人工智能助手提供云存储文件访问能力的服务器组件。 Chris Coutinho Nextcloud MCP Server 0.117.2之前版本存在授权问题漏洞，该漏洞源于WEBHOOK_SECRET默认设置为None且启动验证未要求认证，导致POST /webhooks/nextcloud端点接受未认证请求，且未对payload中的user uid字段进行认证会话交叉检查，可能导致网络攻
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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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