CVE-2025-66454 Arcade MCP Default Hardcoded Worker Secret Allows Full Unauthorized Access to All HTTP MCP Worker Endpoints
Attackers can use a hardcoded default secret to forge JWTs and gain unauthorized access to all Arcade MCP worker endpoints, enabling tool invocation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-66454?
CVE-2025-66454 is a medium-severity vulnerability in ArcadeAI arcade-mcp, published on 2 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Arcade MCP allows you to to create, deploy, and share MCP Servers. Prior to 1.5.4, 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. This vulnerability is fixed in 1.5.4.
Which versions are affected by CVE-2025-66454?
3 open source packages ship an affected version, including arcade-mcp-server.
| Package | Affected | Fixed in |
|---|---|---|
arcade-mcp-server PyPI | All versions | 1.9.1 |
arcade-mcp-server PyPI | All versions | 1.9.1 |
arcade-mcp-server PyPI | All versions | 1.9.1 |
How do I fix CVE-2025-66454?
Upgrade arcade-mcp-server to 1.9.1 or later.
Is CVE-2025-66454 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66454 exists.
Sources
Also known as GHSA-g2jx-37x6-6438, PYSEC-2026-1192.