Banking Trojan Ships With Its Own Certificate

This is all kinds of badness, and speaks to malware vendors becoming increasingly sophisticated in how they are targeting low hanging fruit (i.e. random users). In essence, the attack involved getting a certificate issued and then using it to create valid digital signatures for .pdf invoice documents. Once individuals opened the invoices the malware associated with the .pdf would burrow into the OS and act as a key logger that targeted banking information.

Unfortunately, I’ve not yet seen a media article discuss the mediocre effectiveness of revoking the certificate used to sign the .pdf. The OCSP protocol is incredibly susceptible to being defeated, especially if malware already resides on the target’s computer or a point in between the target and the revocation server is controlled by the attacker (possible by setting a compromised computer to proxy traffic to a host controlled by the attacker). So, while while the cert has been revoked, this actions does not necessarily stop the malware from functioning, but just reduces the prospective attack surface. Moreover, if browser/operating system CA stores are not updated – again, possible if the attacker already controls the host – then the same attacker can convince the browser or OS to continue trusting an expired certificate.