After reading more in https://developer.mastercard.com/open-banking-europe/documentation/licensed/aiia-enterprise/production/tpp-certs/ I noted:
<<< We do not require a pass-phrase for the private key.
[...]
The requirement to set hostname on QWAC certificates is somewhat confusing, as this is a requirement for TLS server certificates, whereas QWAC certificates are TLS client certificates. >>>
WHAT?
From https://crt.sh/?id=12752024628:
<<< X509v3 Extended Key Usage:
TLS Web Client Authentication, TLS Web Server Authentication >>>
If my understanding is correct, an attacker who obtains access to the private key, sends a phishing mail asking to open https:⁄⁄bunq-com.aiiaclient.com and is able to inject falsified DNS replies (or some other possible network-based attacks), can trick users by showing them a fake bunq website - notably using a QWAC?
I surely hope that I misunderstand all of this.
If not: which idiot decided to put a domain name (instead of, for example, an email address) in a QWAC intended for client authentication?
@agl @Tarah @ScottHelme @dangoodin