CVE-2026-55640: CWE-306: Missing Authentication for Critical Function in cbcoutinho nextcloud-mcp-server
Description
Nextcloud MCP Server versions prior to 0.117.2 have a missing authentication vulnerability on the POST /webhooks/nextcloud endpoint. The default configuration allows unauthenticated requests because the WEBHOOK_SECRET is unset by default and not validated at startup. This enables an attacker to send forged webhook payloads that specify arbitrary user IDs, leading to unauthorized deletion or re-indexing of vector embeddings and destruction of the semantic search index. The issue is fixed in version 0.117.2.
CVSS v3.1
Score 9.1critical
Affected software
cbcoutinho
nextcloud-mcp-server
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Nextcloud MCP Server's webhook endpoint /webhooks/nextcloud lacks authentication by default prior to version 0.117.2 due to the WEBHOOK_SECRET environment variable defaulting to None and no startup validation enforcing its presence. This allows unauthenticated attackers to send crafted webhook requests with attacker-controlled user IDs in the payload. These requests can trigger unauthorized Qdrant operations such as deleting or re-indexing vector embeddings for any user and destroying the semantic search index. The vulnerability is identified as CWE-306 (Missing Authentication for Critical Function) and has a CVSS 3.1 score of 9.1, indicating critical severity. The issue is resolved in version 0.117.2.
Potential Impact
An unauthenticated network attacker can exploit this vulnerability to delete or re-index vector embeddings associated with any user in the Nextcloud MCP Server, potentially destroying the semantic search index. This results in high integrity and availability impact on the affected system's search functionality. Confidentiality is not impacted.
Mitigation Recommendations
Upgrade to Nextcloud MCP Server version 0.117.2 or later, where the authentication issue on the /webhooks/nextcloud endpoint is fixed by requiring a valid WEBHOOK_SECRET. Until upgraded, ensure that WEBHOOK_SECRET is set and validated at startup to prevent unauthenticated access. No other mitigations are specified.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-16T23:52:12.057Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a8dbde1acd9273b4969bf95
Added to database: 08/25/2026, 16:08:01 UTC
Last enriched: 09/10/2026, 03:52:37 UTC
Last updated: 10/09/2026, 06:48:18 UTC
Views: 63
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