According to Apple, Safari 7.0.4 for OS X 10.9 Mavericks and Safari 6.1.4 for OS X 10.8 Mountain Lion both address a WebKit flaw in which arbitrary code could be executed on a host computer when visiting a malicious website. The same issue can also cause Safari to unexpectedly crash.
A second problem with WebKit's handling of unicode characters in URLs that allows a maliciously crafted URL to send out false postMessage origins, thus overcoming the receiver's origin check. The issues was resolved through enhanced encoding and decoding.
The latest Safari for OS X versions come a month and a half after the previous Safari 7.0.3 and 6.1.3 updates were released in early April. The older iterations brought granular control over push notifications and support for new top-level domain names like ".cab" and ".clothing."
Safari 7.0.4 and 6.1.4 can be downloaded for free via Software Update.