A friend of a friend received an email from a security researcher that looks legit. Researcher submitted several vulnerabilities, one of the them reads like this
Vulnerability # ...
Title : Lack of wildcard DNS Entry!
Description : The risk of attackers knowing the wildcard which could thus result in DNS Hijacking and further threats. There are several issues related to this. The most common i can think of is phishing. Wildcard DNS is a handy feature, and phishers are apparently using it to bypass filtering. Phishers use wildcard DNS to get around filtering since filtering, in many cases, is based on exact host name and domain name combinations. With wildcard DNS Phishers can generate any number of differing URLs on the fly and often evade filtering technology.
On the Web server side, a simple bit of code can parse the URL to find which hostname was used to land on a site, and then redirect the visitors as necessary.
And there is no wildcard entry so attacker easily enumerate your secret and Public Subdomains.
Then comes a proof of concept with an output from DNS brute-force tool knock.
Just to clarify, the website in question does not have a wildcard (*) in the DNS entry and recursive sub-queries to the DNS are not allowed (e.g. AXFR query doesn't work). The website treats DNS sub-domains as public information anyway. IMO, this is not a vulnerability - it's by design, just want to cross-check with the community.
Question: is lack of a wildcard entry in the DNS a security vulnerability?