OS X Yosemite v10.10.4 and Security Update 2015-005 (for OS X 10.8 Mountain Lion and OS X 10.9 Mavericks), both available from the Mac App Store, address a wide range of security issues.
They include multiple privilege escalation issues, remote attack via AFP, an Apache misconfiguration, multiple PHP issues, multiple examples of kernel memory layout disclosure, multiple memory corruption issues that could be used to execute arbitrary code (including some variously related to fonts, Bluetooth, URL handling, text files, QuickTime, and certain types of signed or encrypted objects), sometimes with system privileges.
Back to OS X, changes to the graphics drivers for Nvidia and Intel perform improved bounds checks to address buffer overflow issues that could allow arbitrary code execution with system privileges.
The certificate trust policy has also been updated, the 'Logjam' SSL/TLS issue has been addressed, the locking of EFI flash memory when waking from sleep has been improved (the EFI patches are available separately as Mac EFI Security Update 2015-001 for Mountain Lion and Mavericks), and certain issues around code signing have been rectified.
A Yosemite-specific change addresses a flaw that allowed unsigned kernel extensions to be loaded under certain conditions.
One of the more curious issues concerns Mail. The version included in Yosemite 10.10.0 to 10.10.3 allowed the content of an HTML message to be replaced with an arbitrary web page.
Another concerns Spotlight, where "A command injection vulnerability existed in the handling of filenames of photos added to the local photo library."
Open source components that have been updated but not already mentioned include libtiff, OpenSSL, SQLite and unzip.
All told, more that 75 distinct vulnerabilities are addressed by OS X Yosemite v10.10.4 and Security Update 2015-005.
The latest version of Safari - 8.0.7 - is included in the OS X Yosemite 10.10.4 update. It is also available separately from the Mac App Store, along with Safari 7.1.7 and 6.2.7 for Mavericks and Mountain Lion respectively.
Changes include improved checking to prevent one site accessing another's WebSQL databases, and better protection against cross-site request forgeries and malicious links in embedded PDFs.
This latest set of updates is consistent with Apple's unstated but apparent policy of only releasing security updates for the current version of OS X and its two most recent predecessors.
In related news, Apple has also released iTunes 12.2 with support for the new Apple Music service. It is available from the Mac App Store.