CVE-2025-59528: Flowise CustomMCP Node JavaScript Function Constructor Remote Code Execution

HERMES

HERMES THREAT SCORE & OPERATIONAL EXPLOITABILITY

Target: Flowise CustomMCP Node Configuration Parser

Confidence: 96%

99 / 100

EXTREME

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 20 / 20

Threat Activity 19 / 20

Weaponization 20 / 20

Exposure 20 / 20

Prevalence 19 / 20

Impact 20 / 20

Exploit Maturity 20 / 20

Attack Chain Potential 20 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates this vulnerability at 10. Hermes Threat Score rates it at 99 (EXTREME) taking into account active exploit telemetry, critical AI workflow dependencies, and immediate host privilege escalation.

HASS

HASS AGENTIC SEVERITY & AUTONOMOUS RISK EVALUATION

Target: Flowise AI Workflow Builder Tool & Memory Architecture

Confidence: 95%

98 / 100

CRITICAL

Measures specific systemic risk arising from autonomy, tool authority, and cascading execution.

Dimension Breakdown

Autonomy 20 / 20

Tool Access 20 / 20

Privilege 20 / 15

Persistence 19 / 15

External Impact 20 / 15

Propagation 20 / 15

⚖️ Divergence & Operational Rationale

Agentic security failure classified under AAP-007 (Tool Hijacking via Insecure MCP Configuration). The flaw collapses trust boundaries between autonomous model reasoning loops and operating system execution tiers.

🕸️ Connected Knowledge Graph & Provenance

CVE-2025-59528: Flowise CustomMCP Node JavaScript Function Constructor Remote Code ExecutionVULNERABILITY

Connected Nodes: 3

Active Relationships (Outgoing)

→ affectsPRODUCTFlowise AI Workflow Builder

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Flowise AI Workflow Builder documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

→ exploitsAGENTIC ATTACK_PATTERNAAP-007: Autonomous Cascading RCE

92% VERY_HIGH

Cascading multi-stage attack chaining context injection, autonomous loop planning, and un-sandboxed execution sinks to achieve persistent root shell compromise on host machines.

🔍 Why is this related? (Evidence & Provenance)

“CVE-2025-59528 weaponizes the agentic attack pattern formalized under AAP-007.”

Supporting Verified Evidence:

• [technical_analysis]Pillar Security demonstrated that executing export BASH_ENV in Auto-Run causes bash to source hostile payloads upon subsequent commands. — Source: Pillar Security Research: Bypassing Cursor Auto-Run: When Shell Built-ins Lead to Host RCE (Reliability: HIGH)

→ usesATTACK TECHNIQUET1059: Command and Scripting Interpreter

90% VERY_HIGH

Adversaries abuse command and script interpreters (Bash, Python, PowerShell) to execute arbitrary commands.

🔍 Why is this related? (Evidence & Provenance)

“Attack execution telemetry aligns with MITRE ATT&CK technique T1059.”

Supporting Verified Evidence:

• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Critical Vulnerability Advisory

CVSS v3.1: 10 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H) / CWE-94: Improper Control of Generation of Code (‘Code Injection’). Addressed in Flowise 3.0.6. Affects deployments running Flowise < 3.0.6.

Executive Summary

Flowise prior to 3.0.6 used the native JavaScript Function() constructor to deserialize the mcpServerConfig configuration string in the CustomMCP node without sanitization. An unauthenticated attacker could supply a malicious MCP configuration payload containing arbitrary JavaScript, achieving full remote code execution in Node.js, stealing master LLM API tokens, and compromising connected infrastructure.

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1. Technical Context & Attack Surface

Flowise AI Workflow Builder is widely deployed in production environments to support large language model orchestration, data pipelines, and agentic workflows. CVE-2025-59528 represents a significant threat to enterprise infrastructure:

Attribute	Technical Specification	Operational Ramification
Vulnerability ID	CVE-2025-59528	Tracked in Hermes Knowledge Graph
Affected System	Flowise AI Workflow Builder	FlowiseAI
Vulnerable Component	Flowise CustomMCP Node Configuration Parser	Input processing & execution gate
Exploit Vector	Network / Local Untrusted Context	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CISA KEV Status	Monitored / High Weaponization Potential	Urgent patching prioritization
Attack Techniques	T1059.007 (Command and Scripting Interpreter: JavaScript), T1190 (Exploit Public-Facing Application)	MITRE ATT&CK Framework
Agentic Attack Pattern	AAP-007 (Tool Hijacking via Insecure MCP Configuration)	Hermes Agentic Security Catalog

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2. Root Cause Analysis & Mechanics

The vulnerability stems from insufficient validation and flawed isolation boundaries in Flowise CustomMCP Node Configuration Parser:

[ Attacker Payload / Untrusted Input ]
                 │
                 ▼
[ Ingress: Flowise CustomMCP Node Configuration Parser ]
                 │  (Missing Canonical Sanitization / Dangerous Evaluation)
                 ▼
[ Execution Tier: Host OS / Runtime Subprocess ]
                 │
                 ▼
[ Impact: Arbitrary Code Execution / Credential Exfiltration ]

When processing requests, the vulnerable logic failed to enforce strict allowlisting or canonical path validation, permitting direct execution or unauthorized file access.

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3. Exploit Scenario & Proof-of-Concept Workflow

Defenders must understand how threat actors weaponize CVE-2025-59528 in real-world intrusion operations:

1. Target Identification & Probing: Adversaries discover exposed instances through version fingerprinting or metadata scraping.
2. Payload Delivery: A crafted request containing the exploit payload is transmitted to the vulnerable endpoint (Flowise CustomMCP Node Configuration Parser).
3. Execution & Breakout: The application executes the payload under the process user permissions, escaping intended sandboxes.
4. Post-Exploitation & Pivot: The attacker harvests LLM API keys, establishes persistence, or moves laterally into connected cloud storage.

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4. Detection Engineering & Hunting Rules

Security Operations Centers (SOC) and incident response teams can deploy the following detection signatures:

Sigma Rule

title: Suspicious Execution from Flowise AI Workflow Builder Subprocess (CVE-2025-59528)
status: experimental
description: Detects abnormal process execution or file creation spawned by Flowise AI Workflow Builder
references:
  - https://codex.hermes-cyber.com/cve/2025/cve-2025-59528/
author: Hermes Cyber Intelligence
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    ParentImage|endswith:
      - '/python'
      - '/node'
      - '/langflow'
      - '/flowise'
    Image|endswith:
      - '/sh'
      - '/bash'
      - '/curl'
      - '/wget'
  condition: selection
falsepositives:
  - Legitimate administrative tooling
level: high

Audit & Hunt Log Query

# Audit suspicious connections and process executions
journalctl -u prod-flowise --since "24 hours ago" | grep -Ei "exec|spawn|attachments|validate"

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5. Remediation & Defensive Hardening

To mitigate exposure to CVE-2025-59528:

1. Immediate Upgrade: Upgrade to Flowise 3.0.6 or later immediately.
2. Network Isolation: Restrict access to administrative interfaces and API listeners via internal VPN or Zero-Trust Network Access (ZTNA).
3. Container Sandboxing: Run workloads with non-root service accounts, read-only root filesystems, and strict seccomp/AppArmor profiles.
4. Credential Rotation: Rotate all LLM provider API keys, database credentials, and cloud secrets that resided in the environment.

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6. Related Intelligence & Playbooks

Agentic Attack Patterns Catalog Explore formal defensive architectures for autonomous AI agents and tool-calling models.

Hermes Threat Observatory Monitor live operational threat intelligence signals and score revisions.