"Runaway inflation" poses the biggest risk to the five-year bull market in stocks, James Paulsen, chief investment strategist at Wells Capital Management, told CNBC on Tuesday. But he put the chances of prices wildly spiraling at about 20 percent.

"If inflation was really getting out of control, you'd have to go then to cash or low-duration bonds or real estate or commodities," Paulsen said in a "Squawk Box" interview. "But I'm not there yet at all. I don't see that as the most likely outlook at the moment."