Dishonest MKR holders have at their disposal two attack vectors.

A game played between stablecoin, CDP, and MKR holders (and also potentially miners)

One of the main things is that the price is calculated by taking the MEDIAN of several Oracles, so no one Oracle can significantly upset the value - it would require many Oracles to be compromised. They were also talking about having a 1 hour delay on prices from oracles in MCD which would allow for an emergency vote to be taken if an attack was occurring.