Vulnerability in nextcloud-mcp-server (CVE-2026-55640)
Summary
Vulnerability in nextcloud-mcp-server (CVE-2026-55640). Data can be tampered with by attackers. Exploitable via POST /webhooks/nextcloud. Mitigation: upgrade to 0.117.2 or later.
Original description
The description as published by the source.
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-T…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55640 has been found in nextcloud-mcp-server.
Attackers can target a specific entry point like POST /webhooks/nextcloud over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 9.1/10.
What to do: upgrade nextcloud-mcp-server to 0.117.2 or later.
If unsure, ask your IT team or search "nextcloud-mcp-server CVE-2026-55640" on the vendor's site.
CVE-2026-55640 (nextcloud-mcp-server) — CWE-306 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: POST /webhooks/nextcloud / WEBHOOK_SECRET / None / user_id
Patched: 0.117.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-306) exists in nextcloud-mcp-server. Attackers reach the vulnerable code path via POST /webhooks/nextcloud without authentication.
Check the vendor advisory for the affected versions of nextcloud-mcp-server. Attack surface: POST /webhooks/nextcloud / WEBHOOK_SECRET / None / user_id.
Severity: Critical (CVSS 9.1/10). Data can be tampered with by attackers.
Update to 0.117.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual POST /webhooks/nextcloud requests with malformed payloads or SQL meta-characters. Run grep -r 'nextcloud-mcp-server' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'nextcloud-mcp-server' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
nextcloud-mcp-serverを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'POST /webhooks/nextcloud' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
POST /webhooks/nextcloudへの異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Apply patch patch
Upgrade nextcloud-mcp-server to 0.117.2ステージング環境で 0.117.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。
-
4Post-deployment verification verify
Replay attack against POST /webhooks/nextcloud on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。