vulnerability / NVI-00013844 / Revision 2
nextcloud-mcp-server: Unauthenticated `POST /webhooks/nextcloud` allows arbitrary vector data deletion when `WEBHOOK_SECRET` is unset ( default )
GitHub lists this reviewed advisory for nextcloud-mcp-server. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
9.1 critical
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
0.730%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.54279. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
nextcloud-mcp-server
source listed<= 0.117.1
## 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**: ```python secret = get_settings().webhook_secret # None by default if secret: # skipped entirely when unset ... validate Bearer header ... else: _warn_missing_secret_once() #
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-8vh3-g2qg-2h2c ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-55640 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.