What was fixed?
The list of software components fixed in the various updates is extensive.
Rather than go into all the details, we'll just encourage you towards grabbing the updates by pointing out that the holes fixed include:
Remote code execution (RCE). Opening a booby-trapped file or browsing to a malicious web page could lead to implanted malware, stolen data and a hijacked computer.
Security bypasses. Files you might expect to be kept away from prying eyes might be visible; secrets useful for further attacks (such as memory addresses used by the operating system) might be revealed.
Denial of service. A crook could force your computer to shut down without warning.
Data leakage. Passwords, private browsing data and application screenshots could be revealed.
Via Gust MEES