First, I would not seek vulnerability-centric solutions. I would not even really seek technological solutions. Instead, I would focus on the threats themselves. Insider threats are humans. They are parties with the capability and intention to exploit a vulnerability in an asset. You absolutely cannot stop all insider threats with technical solutions. You can't even stop most insider threats with technical solutions.
You should focus on non-technical solutions. (Ok, step two is technical.)
- Personnel screening: Know who you are hiring. The more sensitive the position, the deeper the check. The more sensitive the position, the greater the need for periodic reexamination of a person's threat likelihood. This is common for anyone with a federal security clearance, for example.
- Conduct legal monitoring: Make it clear to employees that they are subject to monitoring. The more sensitive the position, the greater the monitoring. Web surfing, email, IM, etc. are subject to inspection and retention within the boundaries of applicable laws.
- Develop and publish security policies: Tell employees what is proper and improper. Let them know the penalties for breaching the policy. Make them resign them annually.
- Discipline, fire, or prosecute offenders: Depending on the scope of an infraction, take the appropriate action. Regulations without enforcement (cough - HIPAA - cough) are worthless.
- Deterrence: Tell employees all of the above regularly. It is important for employees who might dance with the dark side to fully understand the consequences of their misdeeds.
At the end of the day, you should wonder "how many spies?" are there in your organization. Consider the hurdles an insider threat must leap in order to carry out an attack and escape justice.
- He must pass your background check, either by having a clean record or presenting an airtight fake record.
- He must provide a false name and mailing address to frustrate attempts to catch him.
- He must evade detecting by your internal audit systems.
- He must have an escape plan to leave the organization and resurface elsewhere.
I could continue, but imagine those difficulties compared to a remote cyber intruder in Russia who conducts a successful client-side attack on your company? Now which attack is more likely -- the insider or the outsider?