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https://github.com/telekom/OpenAPI-Dissector

This repository contains experimental code for generating an OpenAPI dissector for use within Wireshark.
https://github.com/telekom/OpenAPI-Dissector

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This repository contains experimental code for generating an OpenAPI dissector for use within Wireshark.

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README 

        
# OpenAPI Dissector



This repository contains experimental code for generating an OpenAPI dissector for use within Wireshark.



It was mainly developed for analyzing traffic in 5G core networks, which sends JSON messages over a HTTP/2 API,

but it could potentially be adapted for other APIs as well.



![](doc/screenshot.png)



## Features



- Shows information about operations (summary and filename of specification)

- Validates most of the basic OpenAPI aspects

    - Object properties

    - Simple data types (including value ranges and patterns)

    - Arrays with or without defined item properties

    - etc.

- Supports resolving of specification references (including recursively nested data types)

- Basic support for complex OpenAPI features

    - Support for `anyOf`/`allOf`/`oneOf` keywords, including basic discriminator support

    - Basic support for the `not` keyword (currently only supports forbidden object properties)

    - Reporting incorrectly sent fields which were marked readOnly/writeOnly

- Initial support for callback handling (very limited)

- Links relevant packets inside of the packet details

    - Operations request/response header and data

    - Link between callbacks and source of callback registration (e.g. nnrf subscription and status notifications)

- Highlights packets with found errors inside of Wiresharks packet list

- Prints found errors in packet details



## Installation



### Generate specs file



First step is to generate a specs file (i.e. `openapi_spec.lua`) derived from 3GPP Releases. This can be done using a few commands to clone or copy from 3GPP git (https://forge.3gpp.org/rep/all/5G_APIs) the related yaml files for specific 3GPP-Releases (e.g. 3GPP Rel-17) into the corresponding `specs` sub-directories:



```bash

cd generator/

git clone -b REL-17 https://forge.3gpp.org/rep/all/5G_APIs specs/17.x

git clone -b REL-18 https://forge.3gpp.org/rep/all/5G_APIs specs/18.x

python3 generate.py specs

```



`generate.py` processes each of the 3GPP-Releases specific OpenAPI yaml files (from subdirectories named by release version) and as a result the `openapi_spec.lua` is created in the generator directory.



### Download json library



The dissector code uses a simple JSON library for Lua that can be found [here](https://github.com/rxi/json.lua).



Download the json.lua contained in that repository.



For security reasons, we recommend validating the sha256 checksum of the downloaded file, which as of writing this

documentation (2023-07-26) should be `0eaccda57fabc0330736de25f45cf589821a42b5e0fe02e4e3125f7dc0bf2b7e`.



### Copy required files to wiresharks plugin directory



Inside of Wireshark click on `Help` in the menu bar, and select `About Wireshark`.

In the newly opened window click on the tab `Folders` and look for the entry `Personal Lua Plugins`.



Copy the following files into that directory:



- `openapi_spec.lua` (as generated earlier)

- `json.lua` (as downloaded from the linked project)

- `openapi.lua`

- `json_validator.lua`



## Usage



On launching a new Wireshark instance the plugin should be automatically loaded. Or select in Wireshark the button Analyze->Reload Lua Plugins.



The dissector attaches itself as postdissector to all HTTP/2 packets, so no further configuration is needed as of now.



Now you can apply `openapi` as display filter for Wireshark. 



## Limitations



- Only basic validation of URL parts and no validation for URL query arguments

- Supports only HTTP/2 for now (primary use case was analyzing 5G traffic, which mainly uses HTTP/2 for communication)

- Incomplete support for anyOf/allOf/oneOf/not keywords (because of undefined behaviour in spec)

- No support for predefined data types (e.g. email, uuid, ...)

- Handling of callbacks needs a lot of work, current implementation lacks handling of most of the possible target locations

- Since this is currently a postdissector it can only run on a second pass, which does not happen during Wiresharks live capture mode

- Better error handling (some operations fail silently in Wiresharks Lua environment..)



There are probably a lot more limitations, but at least some of those limitations are due to undefined behaviour

or even conflicts between the OpenAPI and JSON Schema specification. For some of those cases the best way would

probably be to read code of other OpenAPI related projects and implement the behaviour accordingly, but since this

projects exists in the 5G ecosystem we'll probably end up matching the behaviour to align with the 5G specification.



Currently, there is also a bug where sometimes the dissector just doesn't do anything.

This can be worked around by simply reloading the Lua scripts (Ctrl+Shift+L).



## Future improvements



- All of the current limitations should obviously be improved

- Improve handling of missing HTTP/2 header fields (due to compression in HTTP/2 combined with eventually missing packets in pcap)

- Implementing HTTP/1.x support

- Easy filtering on data inside of OpenAPI packets (currently only possible using a regex workaround)

- Better Multi-Version support (currently a single selectable version is used over all NFs and connections, no support for mixed versions)

- Manual selection of correct operation on potential mismatch

- Implement some logic to match specification documents to the correct services (should improve both speed and overall detection of used operations)



At least some of those improvements may need implementation of GUI elements or even a C-extension for wireshark.



## Troubleshooting



### Missing `rex_pcre2` library



It seems that the Lua interpreter bundled with Wireshark releases included in

at least some Ubuntu versions doesn't contain the `rex_pcre2` library.



To solve this issue you can manually install the library:



```

apt install lua-rex-pcre2

```



## License



Copyright (c) 2023 Deutsche Telekom AG.



Licensed under the GNU General Public License Version 2.0 (or later) (the "License"); you may not use this file except in compliance with the License.



You may obtain a copy of the License by reviewing the file [LICENSE](./LICENSE) in the repository or by downloading the respective version from

https://www.gnu.org/licenses/



Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the [LICENSE](./LICENSE) for the specific language governing permissions and limitations under the License.