CVE-2026-58057: Flowise Windows Environment Variable Bypass Leading to Code Execution

Technical summary

CVE-2026-58057 is a case-sensitivity bypass in Flowise versions prior to 3.1.3 affecting Windows deployments. The vulnerability exists in the Custom MCP (Model Context Protocol) stdio environment variable validation logic, which uses case-sensitive comparison against a denylist that includes 'NODE_OPTIONS'. On Windows, where environment variable names are inherently case-insensitive, an authenticated user can supply 'node_options' (lowercase) to circumvent the restriction. This allows injection of Node.js startup flags such as --require, enabling arbitrary code execution within the Flowise server process. The underlying issue is CWE-178 (Improper Handling of Case Sensitivity), stemming from a cross-platform assumption that fails on case-insensitive filesystems.

Business impact

An internal user or contractor with workflow configuration permissions can compromise the Flowise server and any systems it connects to. This is particularly concerning in organizations using Flowise for production AI automation, as code execution occurs with server privileges and can lead to unauthorized access to connected data sources, APIs, and downstream systems. The impact is moderated by the requirement for prior authentication, but the attack surface includes any user granted workflow-building capabilities.

Affected systems

Flowise versions before 3.1.3 running on Windows are affected. The vulnerability does not impact Linux or macOS deployments, as those operating systems enforce case-sensitive environment variable handling, which maintains the denylist's effectiveness. Organizations using Flowise on Windows for AI workflow automation should prioritize patching.

Exploitability

Exploitability requires valid credentials and access to the Custom MCP node configuration interface within Flowise. No complex setup or user interaction is needed beyond configuration permissions. The attack is straightforward once the bypass is understood: a user simply enters 'node_options' instead of 'NODE_OPTIONS' in the environment variable field, then appends a --require flag pointing to arbitrary code. The CVSS score of 5.0 reflects this moderate difficulty (requires authentication and environment-specific conditions on Windows), though organizations should not underestimate the insider risk if workforce access is not tightly controlled.

Remediation

Upgrade Flowise to version 3.1.3 or later, which implements case-insensitive denylist comparison across all platforms. Verify the patch against the official vendor advisory before deployment. As an interim measure on Windows systems, restrict workflow configuration permissions to highly trusted users and monitor Node process creation for unexpected --require or --load-extra-modules flags.

Patch guidance

Apply Flowise 3.1.3 or newer. The patch corrects the validation logic to normalize environment variable names to uppercase (or use case-insensitive comparison) before checking against the denylist. After patching, review existing workflow configurations to identify any that may have exploited this bypass. Test in a non-production environment first to ensure compatibility with custom integrations.

Detection guidance

Monitor Flowise server logs and Node.js process creation events for unusual patterns: (1) NODE_OPTIONS or node_options environment variables being set via Flowise configuration; (2) node processes spawned with --require, --load-extra-modules, or other code-loading flags; (3) Custom MCP nodes with environment variables containing paths to external scripts or suspicious patterns. On Windows, enable detailed process auditing to capture environment variable injection attempts. Check Flowise audit logs for modifications to Custom MCP node configurations by users with non-administrative roles.

Why prioritize this

Although the CVSS is 5.0 (MEDIUM), this vulnerability merits prompt attention in Windows-based deployments because it combines authenticated code execution with a plausible insider threat vector. Organizations should prioritize based on: (1) whether Flowise runs on Windows in your infrastructure; (2) the number of users with workflow configuration access; (3) the sensitivity of systems Flowise integrates with. Those using Flowise in development or sandboxed environments can defer slightly longer; production instances handling sensitive data should patch in the next maintenance window.

Risk score, explained

The CVSS 3.1 score of 5.0 (MEDIUM) reflects the attack vector (network-accessible), required privilege level (low—authenticated user), and lack of user interaction. The score is not elevated to HIGH because exploitation requires prior authentication and is limited to the Flowise server context (not spreading laterally by default). However, the actual risk in your environment depends on how many staff can configure workflows and what data Flowise accesses.

Frequently asked questions