Apple has released updates to its distribution of Java for both Leopard and Snow Leopard. The Java for Mac OS X 10.5 Update 6 release fixes more than two dozen vulnerabilities in Java. Multiple vulnerabilities are fixed "which may allow an untrusted Java applet to obtain elevated privileges," and one issue is fixed where "An expired certificate for a Java applet is treated as valid." The Java for Mac OS X 10.6 Update 1 fixes similar vulnerabilities.
The updates are respectively 122 MB and 78 MB, and can be downloaded via Software Update or from Apple's downloads page.