[pyjug]

>Domains that resolve to private IPs: attacker could set up foo.com which resolves to a private IP

There's a clever extension to this attack; a naive way to mitigate it is to do a DNS resolution first to verify it's not a private IP and then do the actual request. An attacker can simply return a public IP on the first DNS resolution (with a 0 TTY) and then return a private IP on the second. This is called a "TOCTOU" (time-of-check time-of-use) vulnerability. I've written about this and other security best practices on my blog here - https://www.ameyalokare.com/technology/webhooks/2021/05/03/s...

I've also built an egress proxy that prevents such attacks here - https://github.com/juggernaut/webhook-sentry

Same caveat applies, use at your own risk :-)

[tasn]

Yeah, resolving twice is a really bad idea. A good rule of thumb for security: if you think you have a clever hack (e.g. checking DNS twice as a workaround to not being able to patch DNS resolution), it probably isn't so clever as you think.