GHSA-xc48-889x-5qmw: Flowise: CVE-2025-8943 Patch Bypass: npm_config_yes bypasses MCP environment variable blocklist (Unauthenticated RCE)

Summary The mitigation shipped for CVE-2025-8943 blocks the -y and --yes flags on npx to stop auto-installation of arbitrary packages. That flag filter works. The environment-variable check in the same patch denies only four variable names by exact string match, and npm reads its configuration directly from npm_config_* environment variables. Setting npm_config_yes=true reproduces the --yes behaviour the flag filter is meant to prevent, so npx auto-installs and executes the named package. The mitigation is fully bypassed. This works with the MCP security check enabled (CUSTOM_MCP_SECURITY_CHECK=true). On a default Flowise deployment, which ships with no authentication, the result is unauthenticated remote code execution. Root cause The patch treats this as a flag-filtering problem, but the behaviour gated by --yes is also reachable through npm's environment-based configuration. The same is true for the other permitted interpreters, node and python3. A denylist of variable names cannot enumerate every environment variable that alters execution, so the control is incomplete by construction. The fix is to allowlist (or strip) the environment before it reaches the child process, not to extend the denylist. Affected version Flowise 3.1.1, current as of 2026-03-29. Details Validation happens in packages/components/nodes/tools/MCP/core.ts. Two functions run in sequence before any MCP server launches: validateCommandFlags and validateEnvironmentVariables. validateCommandFlags is thorough. It blocks -y and --yes along with a comprehensive set of dangerous flags across npx, node, python, python3, and docker. That part of the patch is sound. The gap is in validateEnvironmentVariables: export const validateEnvironmentVariables = (env: Record<string, any>): void => { const dangerousEnvVars = ['PATH', 'LD_LIBRARY_PATH', 'DYLD_LIBRARY_PATH', 'NODE_OPTIONS'] for (const [key, value] of Object.entries(env)) { if (dangerousEnvVars.includes(key)) { throw new Error(Environmen