# Pentesting gRPC-Web

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## **Manipulation von gRPC-Web-Payloads**

gRPC-Web verwendet Content-Type: `application/grpc-web-text` in Anfragen, was eine Art protobuf in base64-kodierter Form ist. Sie können das Tool [gprc-coder](https://github.com/nxenon/grpc-pentest-suite) verwenden, und Sie können auch seine [Burp Suite Extension](https://github.com/nxenon/grpc-pentest-suite) installieren.

### **Manuell mit dem gGRPC Coder Tool**

1. Zuerst dekodieren Sie den Payload:
```bash
echo "AAAAABYSC0FtaW4gTmFzaXJpGDY6BVhlbm9u" | python3 grpc-coder.py --decode --type grpc-web-text | protoscope > out.txt
```
2. Bearbeiten Sie den Inhalt der decodierten Nutzlast
```
nano out.txt
2: {"Amin Nasiri Xenon GRPC"}
3: 54
7: {"<script>alert(origin)</script>"}
```
3. Kodieren Sie die neue Payload
```bash
protoscope -s out.txt | python3 grpc-coder.py --encode --type grpc-web-text
```
4. Verwenden Sie die Ausgabe im Burp-Interceptor:
```
AAAAADoSFkFtaW4gTmFzaXJpIFhlbm9uIEdSUEMYNjoePHNjcmlwdD5hbGVydChvcmlnaW4pPC9zY3JpcHQ+
```
### **Handbuch mit gRPC-Web Coder Burp Suite Erweiterung**

Sie können die gRPC-Web Coder Burp Suite Erweiterung im [gRPC-Web Pentest Suite](https://github.com/nxenon/grpc-pentest-suite) verwenden, was einfacher ist. Sie können die Installations- und Nutzungshinweise in seinem Repository lesen.

## **Analyse von gRPC-Web Javascript-Dateien**

Es gibt mindestens eine Javascript-Datei in jeder gRPC-Web-Anwendung. Sie können die Datei analysieren, um neue Nachrichten, Endpunkte und Dienste zu finden. Versuchen Sie, das Tool [gRPC-Scan](https://github.com/nxenon/grpc-pentest-suite) zu verwenden.

1. Laden Sie die Javascript gRPC-Web Datei herunter
2. Scannen Sie sie mit grpc-scan.py:
```bash
python3 grpc-scan.py --file main.js
```
3. Analysiere die Ausgabe und teste die neuen Endpunkte und neuen Dienste:
```
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            |
+--------------+----------------+--------------+
```
## Referenzen

- [Hacking into gRPC-Web Artikel von 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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