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Critical, CVSS 9.1amended

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

CVE-2026-55640GHSA-8vh3-g2qg-2h2c

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (nextcloud-mcp-server 0.117.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
EPSS
  • CVE-2026-55640: 0.73% estimated exploitation activity in the next 30 days; percentile 54.32 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The POST /webhooks/nextcloud endpoint has no authentication by default: WEBHOOKSECRET defaults to None and is never required by startup validation. When unset, the receiver accepts any unauthenticated POST. The userid 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: nextcloudmcpserver/vector/webhookreceiver.py, function handlenextcloudwebhook(), lines 55-67 Root cause 1: Auth check is guarded by if secret: - skipped entirely when WEBHOOKSECRET is unset. Root cause 2: webhooksecret: str | None = None in config - no startup validator enforces it, even when vector sync is enabled. Trusted field: payload["user"]["uid"] in webhookparser.py is used as-is for all Qdrant operations - no cross-check against an authenticated session. webhookreceiver.py, lines 55-67: webhookparser.py, line 57: PoC No credentials required. Works on any deployment…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-8vh3-g2qg-2h2c

  2. Revision 2 · amended ·

    Amended from osv record GHSA-8vh3-g2qg-2h2c

  3. Revision 1 · created ·

    Published from ghsa record GHSA-8vh3-g2qg-2h2c

Agent brief

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# Patch Next advisory brief: CVE-2026-55640

Advisory: nextcloud-mcp-server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )
IDs: CVE-2026-55640, GHSA-8vh3-g2qg-2h2c
Record: https://patchnext.com/advisories/cve-2026-55640 (revision 3, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nextcloud-mcp-server 0.117.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nextcloud-mcp-server: affected <= 0.117.1; fixed in 0.117.2

## Suggested inspection (read-only)
- `python -m pip show nextcloud-mcp-server`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nextcloud-mcp-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8vh3-g2qg-2h2c (GitHub-reviewed advisory GHSA-8vh3-g2qg-2h2c lists affected ranges: PyPI nextcloud-mcp-server >=0 <=0.117.1)
- Verified: https://osv.dev/vulnerability/GHSA-8vh3-g2qg-2h2c (OSV record GHSA-8vh3-g2qg-2h2c lists affected ranges: PyPI nextcloud-mcp-server >=0 <0.117.2 (fixed))

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