CVE-2026-55640

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data tampering, service disruption.

Exploit odds

0.7% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-25 16:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-09 21:07 UTC Last updatedMost recent change to the record

Details

Published

2026-08-25 16:16 UTC

Last modified

2026-09-09 21:07 UTC

Exploit probability

0.7% · EPSS, next 30 days

Weakness

CWE-306 · Missing authentication

Record status

Deferred

Attack profile CVSS 3.1 · 9.1

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

High