gcdRadar
archive/Patch now/AIR-2026-1294
closedclosed 25 Aug 2026Patch now2 Disclosed vulnerabilityAI

CVE-2026-55640: Nextcloud MCP Server unauthenticated webhook vulnerability

Nextcloud MCP Server

Nextcloud MCP Server before version 0.117.2 lacks authentication on its webhook endpoint when configured with default settings. An attacker can exploit this to send unauthenticated requests and manipulate user identifiers.

disclosed CVENo confirmed exploitation, so this record is tracked as a disclosed vulnerability and not counted as an incident. It moves into the counts if CISA or the vendor confirms exploitation. Why

CVSS
9.1
EPSS
0.01 · top 46% · 2026-11-13
EPSS scores by FIRST
fix status
Fix status unknown
first report
25 Aug 2026
last update
25 Aug 2026
CVE ids
CVE-2026-55640other records

Timeline · 1

  1. 25 Aug 2026CVE-2026-55640: Nextcloud MCP Server is a production-ready MCP server that connects AI assistants to a Nextcloud instance.

Sources · 1

Advisories and databases

  1. 2026-08-25
    CVE-2026-55640: Nextcloud MCP Server is a production-ready MCP server that connects AI assistants to a Nextcloud instance.
    NVD · nvd.nist.gov/vuln/detail/CVE-2026-55640

Titles and links belong to their publishers. The summary above is written by gcdRadar in its own words; data is CC BY-SA 4.0.

Classification

lane
Patch now
AI role
Attack on AI
categories
Infrastructure vulnerability
severity
2 · Disclosed vulnerability
fix status
Fix status unknown
targets
Framework / tooling
owasp llm top 10
LLM03:2025 Supply Chain
mitre atlas
no technique for these categories
tags
mcpauthentication-bypass
dates
happened 25 Aug 2026 · first reported 25 Aug 2026
origin
NVD
Vulnerability record from NVD / the GitHub Advisory Database. This product uses the NVD API but is not endorsed or certified by the NVD.
record
confidence 0.95 · created 2026-10-18 10:04Z · updated 2026-10-18 10:04Z

Lane, AI role, categories and severity come from the classifier; the OWASP and ATLAS rows are derived from the categories. How these are assigned

Copy a brief

This record as a short Markdown brief, for a ticket, a chat or a coding agent.

the brief as text
# CVE-2026-55640: Nextcloud MCP Server unauthenticated webhook vulnerability

https://gcdradar.vercel.app/incidents/cve-2026-55640-nextcloud-mcp-server-unauthenticated-webhook · AIR-2026-1294 · closed 2026-08-25

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2026-08-25
- AI role: Attack on AI
- Products: Nextcloud MCP Server
- CVE ids: CVE-2026-55640
- CVSS: 9.1

## Summary

Nextcloud MCP Server before version 0.117.2 lacks authentication on its webhook endpoint when configured with default settings. An attacker can exploit this to send unauthenticated requests and manipulate user identifiers.

## What to do

No action recorded; read the sources below and the vendor's advisory.

## Latest updates

- 2026-08-25: CVE-2026-55640: Nextcloud MCP Server is a production-ready MCP server that connects AI assistants to a Nextcloud instance. (https://nvd.nist.gov/vuln/detail/CVE-2026-55640)

## Sources

- 2026-08-25 NVD: CVE-2026-55640: Nextcloud MCP Server is a production-ready MCP server that connects AI assistants to a Nextcloud instance. https://nvd.nist.gov/vuln/detail/CVE-2026-55640

Verify against the vendor's advisory before changing production. Data CC BY-SA 4.0, https://gcdradar.vercel.app.

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