SEPTEMBER 17, 2026
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Case File

CVE-2026-55640

CRITICAL · CVSS 9.1 EPSS 0.48% Public Exploit

Source: NVD + CISA KEV + EPSS · Published 2026-08-25 · Last synced 2026-09-17

CyberRota Analysis

AI-Generated

The Nextcloud MCP Server is vulnerable due to a lack of authentication on the POST /webhooks/nextcloud endpoint, allowing unauthenticated requests to manipulate user data. This flaw enables attackers to delete or re-index vector embeddings, potentially compromising the integrity of the semantic search index. Organizations using versions prior to 0.117.2 should prioritize updating to mitigate the risk of unauthorized data manipulation.

Public Exploit Signal

A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.

Note: these links are listed for security research and verification purposes only.

CVE
CVE-2026-55640
Severity
CRITICAL
CVSS
9.1
EPSS
0.48%

Original NVD 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.