# Pentesting gRPC-Web
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## **Manipulando Cargas 脷tiles de gRPC-Web**
gRPC-Web utiliza Content-Type: `application/grpc-web-text` en las solicitudes, que es una especie de protobuf en forma codificada en base64. Puedes usar la herramienta [gprc-coder](https://github.com/nxenon/grpc-pentest-suite) y tambi茅n puedes instalar su [Extensi贸n de Burp Suite](https://github.com/nxenon/grpc-pentest-suite).
### **Manual con la Herramienta gGRPC Coder**
1. Primero decodifica la carga 煤til:
```bash
echo "AAAAABYSC0FtaW4gTmFzaXJpGDY6BVhlbm9u" | python3 grpc-coder.py --decode --type grpc-web-text | protoscope > out.txt
```
2. Editar el contenido de la carga 煤til decodificada
```
nano out.txt
2: {"Amin Nasiri Xenon GRPC"}
3: 54
7: {""}
```
3. Codifica la nueva carga 煤til
```bash
protoscope -s out.txt | python3 grpc-coder.py --encode --type grpc-web-text
```
4. Utilizar la salida en el interceptor de Burp:
```
AAAAADoSFkFtaW4gTmFzaXJpIFhlbm9uIEdSUEMYNjoePHNjcmlwdD5hbGVydChvcmlnaW4pPC9zY3JpcHQ+
```
### **Manual con la extensi贸n gRPC-Web Coder de Burp Suite**
Puedes usar la extensi贸n gRPC-Web Coder de Burp Suite en [gRPC-Web Pentest Suite](https://github.com/nxenon/grpc-pentest-suite) que es m谩s f谩cil. Puedes leer las instrucciones de instalaci贸n y uso en su repositorio.
## **Analizando archivos Javascript de gRPC-Web**
Hay al menos un archivo Javascript en cada aplicaci贸n gRPC-Web. Puedes analizar el archivo para encontrar nuevos mensajes, endpoints y servicios. Intenta usar la herramienta [gRPC-Scan](https://github.com/nxenon/grpc-pentest-suite).
1. Descarga el archivo Javascript gRPC-Web
2. Escan茅alo con grpc-scan.py:
```bash
python3 grpc-scan.py --file main.js
```
3. Analiza la salida y prueba los nuevos endpoints y nuevos servicios:
```
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 |
+--------------+----------------+--------------+
```
## Referencias
* [Art铆culo sobre Hacking en gRPC-Web por Amin Nasiri](https://infosecwriteups.com/hacking-into-grpc-web-a54053757a45)
* [Suite de Pentest de gRPC-Web](https://github.com/nxenon/grpc-pentest-suite)
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