Subdomain takeover of v.zego.com

How it was found

Summary

v.zego.com points to an AWS EC2 instance at 52.214.138.192 that no longer exists. I was able to take control of this IP address and run my own EC2 instance. I can now serve content on this domain, obtain a TLS certificate for this domain, etc.

If any customers or servers are pointing to anything within this domain, I could serve them arbitrary/malicious content. I could also use this in case your domain whitelists your own domain for OAuth, or if there are cookies scoped to the entire domain. Usually this can have a high impact.

PoC

% dig +short v.zego.com
52.214.138.192

% curl v.zego.com
<!-- hackerone.com/ian -->

Impact

Subdomain takeover