The Federal Reserve is signaling potentially vulnerable spots in the financial system, citing U.S. businesses' debt at the highest levels in more than two decades and risky debt growing.

The Fed's report issued Wednesday was its first assessing the stability of the U.S. financial system. Ten years after the financial crisis, the new report points to excessive borrowing by households and businesses, banks' elevated debt levels, and high prices for stocks and other assets exceeding their real value.

Debt owed by businesses is at historically high levels, and growth in riskier forms of business debt has picked up recently, now at more than $2 trillion, the report says. Some banks' level of debt over assets is near its highest mark in more than 20 years.