Re: GWT: Deserialize objects sent/received via websocket

[an . schall]

Hi everyone,

thanks for all the thoughts about the topic. After further investigation of the 
protocol, it seems like there is no pbject serialization involved. Instead, the 
application creates a websocket and establishes a AES-CBC encrypted channel. 
Hence, the binary blobs that I was seeing are encrypted messages. If somebody 
is interested, the website is https://metatraderweb.app/trade

Thanks again!

On 20.10.23 20:12, Colin Alworth  wrote:
Seeing traffic wouldn't hurt, but it would be easiest to discover by 
looking at code - finding "WebSocket" in the codebase, then seeing what 
the import is. Alternatively, the compiled JS will probably have some 
hints, depending on how it was built.


As to the authentication approach you clarified - if the client sends a 
POST before the websocket is created that performs the authentication, 
it is quite likely that the server responds by setting a cookie, and 
that all subsequent HTTP requests (including the websocket) are 
authenticated with that cookie. It is also possible that the websocket's 
binary blobs contain the credentials again, or more likely, the session ID.


gRPC is indeed typically binary protobuf data... but gRPC can't be used 
in a browser in 2023. gRPC-web is a thing... which can't stream binary 
data, and can't stream data to the server (using the tooling provided by 
the gRPC project itself). There are alternative gRPC-web clients that 
can support streaming binary data _from_ the server, but in 2023 the 
fetch() API is still server streaming only, even with h2. There are even 
really-alternative gRPC clients for the browser that rely on websockets 
as well, but if you get in a situation where you want more than a small 
handful of concurrent streams the browser just hangs on new calls, so I 
can't recommend that, unless you use the websocket to replace the h2 
transport rather than using it per-stream (but now you've got more work 
to make sure you clean up streams promptly, and they aren't a lot of fun 
to debug).

On Friday, October 20, 2023 at 12:59:15 PM UTC-5 Thomas Broyer wrote:

You could have a look at
https://docs.google.com/document/d/1eG0YocsYYbNAtivkLtcaiEE5IOF5u4LUol8-LL0TIKU/edit 
 to 
see what GWT-RPC exchanges look like and see if they match what you're seeing. But they're not 
"binary".

I didn't follow what gRPC (Google's RPC format: https://grpc.io/
) looks like on the web, but it's possible they
use "binary" nowadays.

On Friday, October 20, 2023 at 3:10:17 PM UTC+2 an.s...@gmail.com wrote:

Dear Colin,

thanks for the quick response. I did observe the authentication
approach via BurpSuite that allows me to investigate each HTTP /
websocket request / response. From this perspective, I can see
that upon submitting my credentials to the webapp, there is only
one HTTP POST request from client-side that only includes the
username. After this initial POST request, all the communication
goes over websocket with binary blobs being exchanged. Hence, it
is not easy for me to identify which GWT library class is in use.

Is there any way how to get this information, (i.e. I could
provide the URL of the endpoint I am talking to).

Best,
André

Colin Alworth schrieb am Freitag, 20. Oktober 2023 um 14:55:53
UTC+2:

While GWT offers websocket support, the only support is "now
you can send messages on a websocket" - no serialization is
offered, beyond what the browser itself provides (allowing
sending a utf8 string, arraybuffers, blobs, typedarrays, or
arrayviews). How are you verifying messages sent/received?
If you are observing some 3-4 websocket frame handshake
messages on the websocket, that is probably some other GWT
library in use - which WebSocket class are you using?

I maintain (and use in production) an rpc-over-websocket
implementation , but
it does not explicitly support authentication. Instead
usually the first message authenticates with the server, or
HTTP headers are used to authenticate (potentially using
existing cookies) before the websocket is even initiated. So
at least we can probably rule out that implementation.

See
https://developer.mozilla.org/en-US/docs/Web/API/WebSocket

for more information on what the browser's own WebSocket
type offers.

On Friday, October 20, 2023 at 7:31:03 AM UTC-5
an.s...@gmail.com wrote:

Hi,

I am very new to GWT and have questions about the basic
 

Re: GWT: Deserialize objects sent/received via websocket

[An Schall]

Dear Colin,

thanks for the quick response. I did observe the authentication approach 
via BurpSuite that allows me to investigate each HTTP / websocket request / 
response. From this perspective, I can see that upon submitting my 
credentials to the webapp, there is only one HTTP POST request from 
client-side that only includes the username. After this initial POST 
request, all the communication goes over websocket with binary blobs being 
exchanged. Hence, it is not easy for me to identify which GWT library class 
is in use.

Is there any way how to get this information, (i.e. I could provide the URL 
of the endpoint I am talking to).

Best,
André

Colin Alworth schrieb am Freitag, 20. Oktober 2023 um 14:55:53 UTC+2:

> While GWT offers websocket support, the only support is "now you can send 
> messages on a websocket" - no serialization is offered, beyond what the 
> browser itself provides (allowing sending a utf8 string, arraybuffers, 
> blobs, typedarrays, or arrayviews). How are you verifying messages 
> sent/received? If you are observing some 3-4 websocket frame handshake 
> messages on the websocket, that is probably some other GWT library in use - 
> which WebSocket class are you using?
>
> I maintain (and use in production) an rpc-over-websocket implementation 
> , but it does not explicitly 
> support authentication. Instead usually the first message authenticates 
> with the server, or HTTP headers are used to authenticate (potentially 
> using existing cookies) before the websocket is even initiated. So at least 
> we can probably rule out that implementation. 
>
> See https://developer.mozilla.org/en-US/docs/Web/API/WebSocket for more 
> information on what the browser's own WebSocket type offers.
>
> On Friday, October 20, 2023 at 7:31:03 AM UTC-5 an.s...@gmail.com wrote:
>
>> Hi,
>>
>> I am very new to GWT and have questions about the basic principles of how 
>> GWT via websockets work.
>>
>> I would like to analyze the authentication function of a given GWT web 
>> application. When authenticating with my credentials, I could identify that 
>> my credentials are sent via websocket in form of a binary blob. This most 
>> certainly is a serialized GWT object. The authentication seems to follow a 
>> protocol that involves 3-4 messages exchanged with the server-side.
>>
>> Hence, I strive to understand how the client-side transforms my textual 
>> credentials (username / password) into this binary blob. Subsequently, I 
>> would like to understand how I can deserialize messages coming from the 
>> server in order to get a better idea of the messages exchanged and hence 
>> the protocol.
>>
>> Thanks,
>>
>> André
>>
>

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GWT: Deserialize objects sent/received via websocket

[An Schall]

 

Hi,

I am very new to GWT and have questions about the basic principles of how 
GWT via websockets work.

I would like to analyze the authentication function of a given GWT web 
application. When authenticating with my credentials, I could identify that 
my credentials are sent via websocket in form of a binary blob. This most 
certainly is a serialized GWT object. The authentication seems to follow a 
protocol that involves 3-4 messages exchanged with the server-side.

Hence, I strive to understand how the client-side transforms my textual 
credentials (username / password) into this binary blob. Subsequently, I 
would like to understand how I can deserialize messages coming from the 
server in order to get a better idea of the messages exchanged and hence 
the protocol.

Thanks,

André

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