CVE-2026-67531FrontMCP: CodeCall sandbox escape -> host RCE via live Zod schema exposure by getTool

Official description

FrontMCP is a TypeScript-first framework for the Model Context Protocol (MCP). Prior to 1.5.7, the sandboxed codecall:execute tool exposes live host Zod schema instances to the script via getTool(), and because Zod v4 defines _zod as a non-configurable, non-writable own property, the ECMAScript Proxy invariants force the security membrane to hand back the raw host object, letting a script reach _zod.constr.constructor (the host Function constructor) and execute arbitrary code in the server process. A single tools/call is sufficient to escape the sandbox and achieve remote code execution as the server user, exposing everything the process holds such as OAuth client secrets, JWT_SECRET, session keys, database credentials, and cloud instance metadata. Because the framework's DEFAULT_AUTH_OPTIONS is public mode, an unconfigured server serves this to unauthenticated callers, and on authenticated servers an indirect prompt injection in tool output or fetched content can trigger it without a human attackerThis issue is fixed in version 1.5.7.

Affected products (as reported)

References

• https://github.com/agentfront/frontmcp/security/advisories/GHSA-mp29-fxh8-92px x_refsource_CONFIRM
• https://github.com/agentfront/frontmcp/commit/209cddd19a8d4db0777f725b527818da7df6f67f x_refsource_MISC