Authorized Fetch Circumvented by Alt-Right Developers

A controversial developer circumvented one of Mastodon's primary tools for blocking bad actors, all so that his servers could connect to Threads.

We’ve criticized the security and privacy mechanisms of Mastodon in the past, but this new development should be eye-opening. Alex Gleason, the former Truth Social developer behind Soapbox and Rebased, has come up with a sneaky workaround to how Authorized Fetch functions: if your domain is blocked for a fetch, just sign it with a different domain name instead.

Gleason was originally investigating Threads federation to determine whether or not a failure to fetch posts indicated a software compatibility issue, or if Threads had blocked his server. After checking some logs and experimenting, he came to a conclusion.

“Fellas,” Gleason writes, “I think threads.net might be blocking some servers already.”

What Alex found was that Threads attempts to verify domain names before allowing access to a resource, a very similar approach to what Authorized Fetch does in Mastodon.

You can see Threads fetching your own server by looking at the facebookexternalua user agent. Try this command on your server:

grep facebookexternalua /var/log/nginx/access.log

If you see logs there, that means Threads is attempting to verify your signatures and allow you to access their data.