Stable value funds are commonly found in 401(k) plans. They're designed to provide yields higher than money market funds without too much more risk. The question of stable value fund safety has been investigated in the past. I found this 2006 New York Times article
on the subject. They have been tested by the 2008/2009 financial crisis. However, they haven't been tested in an environment of rapidly rising interest rates. This My Money Blog post
reviews how such an environment may affect stable value funds, and it also provides a few useful tips if you do hold stable value funds.