Here's the big list, and honestly, this is mostly about linking to posts on Cameron Kaiser's TenFourFox Development blog since he wrote the bash replacement below and knows just as much as anybody:
1) Yes, the
bashthat comes with your PowerPC Mac is compromised. Cameron Kaiser was nice enough to build a new version) that fixes the security flaw so us PowerPC users can rest easy (also works for Snow Leopard).
2) SSLv3 is no longer safe. The solution here is to update TenFourFox and Tenfourbird to their latest versions which disable SSLv3. Webkit browsers that depend on the system SSL libraries remain vulnerable (UPDATE: leopard-webkit now disables SSLv3 as well).
3) Certain versions of OpenSSL have a hole. Older OpenSSL-based libraries bundled with Tiger and Leopard are not vulnerable to this specific bug, but if you have versions 1.0.1 to 1.0.1f installed on your system through Macports or Homebrew/Tigerbrew, you'll want to update to the latest version.
4) That handy tool
sudo, giving you root access from the command line, is vulnerable to an exploit. Check this post for the solution and also look down to the comments on how to use
nanoto correct it in case
viis a mystery to you.
5) Flash is not safe.
6) Java is not safe. I've seen links about installing Open JDK 7 on Leopard, but I don't know how feasible it is. You could also put Debian on a separate partition and run the latest Java from there.
7) Finally, your Firewire ports are vulnerable to physical attack. You can check out Adam Albrec's Security Mode scripts to secure your laptops from this and other vulnerabilities.
As said, this post will be continually updated with developing news. Hopefully the list won't get too long. ;-)
And I've been informed of yet another one. The Diginotar SSL certificate is compromised. This was back in 2011 and was the first time Apple released a security update that didn't include PowerPC, so maybe that's why I blocked it out. Follow the step-by-step instructions at $ ps | Enable (their mpkg automator didn't seem to change things for me) to clear your system. This flaw only affects you if you use Safari or another browser that accesses your system's SSL certificates. It does not effect TenFourFox.
Via TenFourFox Development again, there are potential vulnerabilities in OS X's ntpd (Network Time Protocol daemon). This is used when you sync date and time automatically with Apple's time server in the Date & Time System Preference. I say potential because the typical user won't find themselves vulnerable, but people using ntpd in more elaborate ways should read the referenced blog post. A new version compiled for PowerPC is linked there for download.
Time to get your FREAK on! That's FREAK for "Factoring Attack on RSA-EXPORT Keys." Once again, if you're using TenFourFox you're not vulnerable, but Webkit users are.
This one's called Darwin Nuke and in theory can enable an outsider to trigger kernel panics on your system. I say in theory because Cameron Kaiser reports he's unable to trigger a successful attack against his PowerPC systems. However, since the vulnerable code does exist in the Tiger and Leopard kernels, it's safest to disable all incoming ICMP traffic on your router's firewall. On my Linksys router, this was already disabled by default with the Security --> Firewall setting, "Block Anonymous Internet Requests". If you don't see anything comparable on your router, google your router's brand and "disable ICMP". ICMP is used by network administrators for troubleshooting purposes, so the average user doesn't need it, anyway.
Run this RootPipeTester tool to see if you're vulnerable to something called
systemsetupusthebomb. Read in detail at TenFourFox Development, but the short version is you should open your Security preference pane and check "Require password to unlock each secure system preference" (wording may be slightly different on Leopard), and you'll be secure against all known attacks. For an even more airtight solution, rename your
writeconfigfile according to the instructions Cameron Kaiser laid out on the linked post above.
Turn off Bluetooth, or if your must use it, use it in a controlled environment.