GMS-2019-70: Low severity vulnerability that affects Gw2Sharp

Leaking cached authenticated requests

Impact

If you’ve been using one MemoryCacheMethod object in multiple instances of Gw2WebApiClient and are requesting authenticated endpoints with different access tokens, then you are likely to run into this bug.

When using an instance of MemoryCacheMethod and using it with multiple instances of Gw2WebApiClient, there’s a possibility that cached authenticated responses are leaking to another request to the same endpoint, but with a different Guild Wars 2 access token. The latter request wouldn’t start however, and would return the first cached response immediately. This means that the second response (or later responses) may contain the same data as the first response, therefore leaking data from another authenticated endpoint.

The occurence of this is limited however. The Guild Wars 2 API doesn’t use the Expires header on most (if not all) authenticated endpoints. This header is checked when caching responses. If this header isn’t available, the response isn’t cached at all. You should still update to at least version 0.3.1 in order to be certain that it won’t happen.

Patches

This bug has been fixed in version 0.3.1. When using an authenticated endpoint, it will prepend the SHA-1 hash of the access token to the cache id.

Workarounds

For version 0.3.0 and lower, you can use one separate instance of MemoryCacheMethod per Gw2WebApiClient if you need to use it.

For more information

If you have any questions or comments about this advisory, you can open an issue in the Gw2Sharp repository or contact me on Discord.