Apple on Monday released a large security update for Mac OS X that fixes dozens of vulnerabilities and provides protection against potential attacks exploiting a weakness in the protocol used to verify that a domain is legitimate.

There are 43 specific issues addressed in the 2009-006 update, released the same day as Mac OS X v.10.6.2.

It plugs a variety of holes for the Mac OS X v10.5.8, 10.6, 10.6.1, and Mac OS X Server v10.6 and 10.6.1, many of which could lead to arbitrary code execution and allow an attacker to take control of a computer.

Several updates affect Apache and QuickTime. Others target AFP Client, Apple Type Services, Core Graphics, CoreMedia, Dictionary, Disk Images, Dovecot, Directory Service, fetch mail, FTP Server, Help Viewer, Kernel, PHP, QuickDraw Manager and Spotlight.

One update fixes a hole in Adaptive Firewall that could allow a brute force or dictionary attack to guess an SSH log-in password, and another update addresses a vulnerability in Login Window that could allow a user to log in to any account without supplying a password.

Several updates address holes that could allow domain spoofing or man-in-the-middle attacks involving SSL (Secure Sockets Layer) used for encrypting data in transit, including a significant weakness in the X.509 protocol for generating SSL connections.

One of the updates affects the libsecurity feature and is billed as a "proactive change to protect users in advance of improved attacks against the MD2 hash algorithm" that could expose users to spoofing and information disclosure.

"There are known cryptographic weaknesses in the MD2 hash algorithm. Further research could allow the creation of X.509 certificates with attacker controlled values that are trusted by the system," the update says. "This could expose X.509 based protocols to spoofing, man in the middle attacks, and information disclosure. While it is not yet considered computationally feasible to mount an attack using these weaknesses, this update disables support for an X.509 certificate with an MD2 hash for any use other than as trusted root certificate."

That major weakness was revealed by security researcher Dan Kaminsky at the Defcon hacker conference in July. Kaminsky was able to trick a Certificate Authority into providing a certificate verifying authenticity for a domain that belonged to someone else.

The updates can be downloaded from Apple's site.