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https://github.com/mildsunrise/protobuf-inspector

🕵️ Tool to reverse-engineer Protocol Buffers with unknown definition
https://github.com/mildsunrise/protobuf-inspector

protocol-buffers reverse-engineering serialization

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🕵️ Tool to reverse-engineer Protocol Buffers with unknown definition

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# protobuf-inspector



Simple program that can parse [Google Protobuf][] encoded blobs

(version 2 or 3) without knowing their accompanying definition.

It will print a nice, colored representation of their contents. Example:



![Main screenshot](https://i.imgur.com/Vw403MI.png)



As you can see, the field names are obviously lost, together with

some high-level details such as:



 - whether a varint uses [zig-zag encoding][] or not (will assume no zig-zag by default)

 - whether a 32-bit/64-bit value is an integer or float (both shown by default)

 - signedness (auto-detect by default)



But protobuf-inspector is able to correctly guess the message structure

most of the time. When it finds embedded binary data on a field, it'll

first try to parse it as a message. If that fails, it'll display the data

as a string or hexdump. It can make mistakes, especially with small chunks.



It shows the fields just in the order they are encoded in the

wire, so it can be useful for those wanting to get familiar with

the [wire format][] or parser developers, in addition to reverse-engineering.



## Usage



You can install with pip:



    pip install protobuf-inspector



This installs the `protobuf_inspector` command. Run it, feeding the protobuf blob

on stdin:



    protobuf_inspector < my-protobuf-blob



After reading the first (blind) analysis of the blob, you typically start defining

some of the fields so protobuf-inspector can better parse your blobs, until you get

to a point where you have a full protobuf definition and the parser no longer has

to guess anything.



[Read about defining fields here.](CONFIG.md)



## Parsing errors



If a parsing error is found, parsing will stop *within that field*, but

will go on unaffected at the outside of the hierarchy. The stack trace will

be printed where the field contents would go, along with a hexdump indicating where

parsing was stopped in that chunk, if applicable.



So, if you specified a `uint32` and a larger varint is found, you'd get something like:



![Error on invalid varint](https://i.imgur.com/DWG9MGX.png)



If you specified that some field contained an embedded message, but invalid data was

found there, you'd get:



![Error on invalid message](https://i.imgur.com/URaWqXz.png)



Please note that `main.py` will exit with non-zero status if one or more parsing

errors occurred.



## Tricks



There are some tricks you can use to save time when approaching a blob:



 1. If you are positive that a varint does *not* use zig-zag encoding, but are still

    not sure of the signedness, leave it as `varint`. If it does use zig-zag encoding,

    use `sint64` unless you are sure it's 32-bit and not 64-bit.



 2. If a chunk is wrongly being recognized as a `packed chunk` or an embedded message,

    or if you see something weird with the parsed message and want to see the raw bytes,

    specify a type of `bytes`. Conversely, if for some reason it's not being detected

    as an embedded message and it should, force it to `message` to see the reason.



 3. If you want to extract a chunk's raw data to a file to analyze it better, specify a

    type of `dump` and protobuf-inspector will create `dump.0`, `dump.1`,

    etc. every time it finds a matching blob.



 4. protobuf-inspector parses the blob as a message of type `root`, but that's just a

    default. If you have lots of message types defined, you can pass a type name as

    optional argument, and protobuf-inspector will use that instead of `root`:

    

        protobuf_inspector request < my-protobuf-blob



## Programmatic access



Simple example:



~~~ python

from protobuf_inspector.types import StandardParser



parser = StandardParser()

with open('my-blob', 'rb') as fh:

   output = parser.parse_message(fh, "message")

print(output)

~~~



This project was not initially designed for use as a library, though,

and its API might change. For a more complex example,

see `protobuf_inspector/__main__.py`.



[Google Protobuf]: https://developers.google.com/protocol-buffers

[Wire format]: https://developers.google.com/protocol-buffers/docs/encoding

[Zig-zag encoding]: https://developers.google.com/protocol-buffers/docs/encoding#signed-integers