Apple have just released an update of Lion and Snow Leopard to fix the security issues.
Here’s the release notes:
Available for: Mac OS X v10.6.8, Mac OS X Server v10.6.8, OS X Lion v10.7.1, Lion Server v10.7.1
Impact: An attacker with a privileged network position may intercept user credentials or other sensitive information
Description: Fraudulent certificates were issued by multiple certificate authorities operated by DigiNotar. This issue is addressed by removing DigiNotar from the list of trusted root certificates, from the list of Extended Validation (EV) certificate authorities, and by configuring default system trust settings so that DigiNotar’s certificates, including those issued by other authorities, are not trusted.
Download the update directly from here.