CVE-2026-56274: Flowise OS Command Injection RCE Flaw

CVE-2026-56274 Overview

CVE-2026-56274 is an OS command injection vulnerability in Flowise versions before 3.1.2. The flaw exists in the Custom MCP (Model Context Protocol) Server feature, where the validateCommandFlags blocklist and validateArgsForLocalFileAccess regex checks fail to cover key bypass cases. Any authenticated Flowise user, or any API caller with view/update permissions on chatflows, can configure a malicious MCP server entry that executes arbitrary commands on the Flowise host. The weakness maps to CWE-78: Improper Neutralization of Special Elements used in an OS Command.

Critical Impact
Authenticated attackers can achieve remote code execution on the Flowise host through bypasses in validateCommandFlags (for example, docker build and npx --yes are not blocked) and validateArgsForLocalFileAccess.

Affected Products

FlowiseAI Flowise versions prior to 3.1.2
Deployments exposing the Custom MCP Server feature to authenticated users
Self-hosted Flowise instances reachable from the network with low-privilege accounts

Discovery Timeline

2026-06-23 - CVE-2026-56274 published to NVD
2026-06-24 - Last updated in NVD database

Technical Details for CVE-2026-56274

Vulnerability Analysis

Flowise lets users configure Custom MCP servers by specifying a command and arguments that the backend will spawn. To restrict abuse, Flowise applies two validation layers: validateCommandFlags, which blocks dangerous command and flag combinations, and validateArgsForLocalFileAccess, which uses regular expressions to reject local file system references. Both layers contain gaps that an authenticated attacker can exploit to launch arbitrary binaries with arbitrary arguments under the Flowise process identity.

Because configuration of MCP servers is exposed to any user role and to API tokens with chatflow view or update scopes, the privilege barrier is low. Successful exploitation grants code execution within the Flowise container or host, exposing application secrets, database credentials, connected LLM API keys, and any chatflow data processed by the instance.

Root Cause

The root cause is incomplete denylist-based input validation. validateCommandFlags enumerates specific binaries and flags rather than enforcing an allowlist, so siblings such as docker build slip through. The flag check blocks -y but not the equivalent long form --yes, allowing npx --yes <package> to install and execute attacker-controlled packages. The validateArgsForLocalFileAccess regex similarly fails to canonicalize argument paths, enabling crafted strings to bypass local-file restrictions.

Attack Vector

An attacker authenticates to Flowise with any role, or uses an API key carrying chatflows:view or chatflows:update scope. They create or modify a Custom MCP Server entry whose command and args fields combine an allowed binary with bypass flags, for example invoking npx --yes against a malicious package or invoking docker build against a crafted context. When Flowise spawns the MCP child process, the supplied command executes on the host, yielding arbitrary code execution. See the GitHub Security Advisory GHSA-m99r-2hxc-cp3q and the VulnCheck Advisory on Flowise for technical specifics.

Detection Methods for CVE-2026-56274

Indicators of Compromise

Unexpected child processes spawned by the Flowise Node.js process, such as npx, docker, sh, or bash.
Outbound network connections from the Flowise host to package registries or attacker infrastructure shortly after MCP configuration changes.
New or modified Custom MCP Server entries containing flags like --yes, build, or argument strings that reference local paths or remote URLs.
Audit log entries showing chatflow update API calls from low-privilege users or service tokens followed by MCP execution events.

Detection Strategies

Monitor process lineage on Flowise hosts and alert on the Flowise runtime spawning shells, package managers, or container tooling.
Inspect Flowise application logs and database tables that store MCP server definitions for command strings containing npx --yes, docker build, or similar patterns.
Correlate authentication events with MCP configuration writes to flag low-privilege accounts performing administrative-style changes.

Monitoring Recommendations

Forward Flowise application, container, and host process telemetry to a centralized analytics platform for behavioral baselining.
Track egress from the Flowise host and alert on connections to public package registries that are not part of normal operation.
Review chatflow API token scopes regularly and alert when tokens with update scope create or change MCP server entries.

How to Mitigate CVE-2026-56274

Immediate Actions Required

Upgrade Flowise to version 3.1.2 or later, which closes the validateCommandFlags and validateArgsForLocalFileAccess bypasses.
Audit existing Custom MCP Server entries and remove any that were not created by trusted administrators.
Rotate Flowise API keys, database credentials, and any LLM provider keys stored on the host that may have been exposed.
Restrict Flowise account creation and reduce the population of users holding any role until patching completes.

Patch Information

Upgrade to Flowise 3.1.2 or later. The fix tightens the command and argument validation logic in the Custom MCP Server pathway. Refer to the GitHub Security Advisory GHSA-m99r-2hxc-cp3q for the official remediation details.

Workarounds

Place Flowise behind network controls that limit administrative and API access to trusted operators only.
Disable or remove the Custom MCP Server feature in environments where it is not required until the patch is applied.
Run Flowise as a non-root user inside a hardened container with a read-only file system and restricted egress to limit blast radius if exploitation occurs.
Revoke API tokens carrying chatflows:update scope from non-administrative integrations.

bash

# Configuration example: upgrade and constrain Flowise deployment
npm install -g flowise@3.1.2

# Run with a dedicated low-privilege user and restricted egress
docker run --rm \
  --user 1001:1001 \
  --read-only \
  --cap-drop=ALL \
  --network flowise-restricted \
  -e DISABLE_FLOWISE_TELEMETRY=true \
  -p 3000:3000 \
  flowiseai/flowise:3.1.2