burp-protobuf-decoder

A simple Google Protobuf Decoder for Burp

Prerequisites

In Burp Store, install the Protobuf Decoder extension.

Why can't I edit a decoded proto message?

Serializing a message requires a proto file descriptor (*.proto file). Without this proto, we don't know how fields should be serialized.
What if I have a proto file descriptor?

Load it from a Protobuf tab by right-clicking. Messages will be automatically decoded from then on. If you wish to manually deserialize a message as different type, this option is available to you via a right-click context menu once a proto is loaded.

By loading a .proto, you can edit and tamper protobuf messages. The extension will automatically serialize messages back before they're sent along.
Can I deserialize protobufs passed as URL or form parameters?

Yes, you can. In the 'Protobuf Decoder' tab, add a parameter to the table. You can specify additional pre and post processing rules, to handle base64 encoding or zlib compression. Don't forget to check the enabled box for each rule once you're done.

Note, the editor tab window may not immediately pick up the changes. You can work around this issue by cycling through requests (anything that'd trigger the editor tab to reload itself)

Since Java doesn't support methods larger than 64k, big proto definitions need to be spit in multiple files. Otherwise, you get the error "Method code too large"
proto2 files should always declare syntax = “proto2” in the header instead of leaving it implicit, otherwise it won't work since the default is proto v3