GHSA-g2jx-37x6-6438 is a medium-severity (CVSS 6.5) CWE-321 vulnerability in arcade-mcp-server. A fix is available for arcade-mcp-server — see the affected versions and patch details below.
arcade-mcp-server Has Default Hardcoded Worker Secret That Allows Full Unauthorized Access to All HTTP MCP Worker Endpoints
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-g2jx-37x6-6438.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-g2jx-37x6-6438 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
arcade-mcp-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The arcade-mcp HTTP server uses a hardcoded default worker secret ("dev") that is never validated or overridden during normal server startup. As a result, any unauthenticated attacker who knows this default key can forge valid JWTs and fully bypass the FastAPI authentication layer. This grants remote access to all worker endpoints—including tool enumeration and tool invocation—without credentials.
Anyone following the official quick-start guide is vulnerable unless they manually override ARCADE_WORKER_SECRET.
Details
The documented method for launching an HTTP MCP server (python server.py http) implicitly sets the worker secret to the hardcoded default "dev":
ArcadeSettings.server_secret defaults to "dev" (libs/arcade-mcp-server/arcade_mcp_server/settings.py:129–158)
create_arcade_mcp() passes this value directly to FastAPIWorker without validation (libs/arcade-mcp-server/arcade_mcp_server/worker.py:118–188)
BaseWorker._set_secret() accepts this value and does not enforce rotation (libs/arcade-serve/arcade_serve/core/base.py:42–83)
Because the worker’s signing key is constant and publicly documented, attackers can trivially generate valid HS256 JWTs:
The FastAPI worker auth middleware (arcade_serve/fastapi/auth.py) trusts any JWT signed with the worker secret.
The core auth layer (arcade_serve/core/auth.py) does not distinguish forged tokens from legitimate ones.
The official quick-start instructions (README.md:164–190) demonstrate launching an MCP server without mentioning worker-secret rotation. Users are told how to define tool secrets in .env, but not that the worker’s authentication key must be changed.
As a result, servers deployed following the documented workflow expose all /worker/* endpoints to anyone capable of generating a simple HS256 token using the known key.
This CVE was resolved by https://github.com/ArcadeAI/arcade-mcp/pull/691
PoC
Start the server using the official guide https://docs.arcade.dev/en/home/build-tools/create-a-mcp-server
Verify that unauthenticated access is rejected (expected)
curl -s -D - http://127.0.0.1:8000/worker/tools
# → 403 Forbidden
Forge a valid HS256 token using the hardcoded default secret "dev"
import jwt
print(jwt.encode({'ver': '1', 'aud': 'worker'}, 'dev', algorithm='HS256'))
Use the forged token to bypass authentication
curl -s -D - \
-H "Authorization: Bearer $(cat /tmp/forged_token.txt)" \
http://127.0.0.1:8000/worker/tools
Result: The server responds 200 OK with the full tool catalog and allows invocation of all worker tools.
Server logs show a rejected request immediately followed by a successful forged request, confirming the bypass.
Impact
This is an authentication bypass that results in full remote access to all MCP worker endpoints:
Unauthenticated attackers can enumerate tools
Invoke arbitrary tools remotely
Access any data returned by tools (including secrets loaded into ToolContext)
Execute actions inside internal systems if tools expose operational capabilities
Perform these actions without any brute forcing or guesswork due to the known default signing key
Any user who follows the official setup guide is exposed unless they manually override ARCADE_WORKER_SECRET, which is not documented.
This vulnerability effectively gives complete remote control over the MCP worker API to any attacker aware of the default key.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | arcade-mcp-server | all versions | 1.9.1pip install --upgrade 'arcade-mcp-server==1.9.1' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for arcade-mcp-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update arcade-mcp-server to 1.9.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-g2jx-37x6-6438 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-g2jx-37x6-6438 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-g2jx-37x6-6438. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-g2jx-37x6-6438 in your dependencies?
O3 Security finds GHSA-g2jx-37x6-6438 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.