Mobile Device Security and Android File Disclosure

Originally Posted by jduck

Back in November, Thomas Cannon brought to light an issue within the Android operating system. Specifically, he found that it was possible to obtain the contents of files on an Android device by simply persuading its owner to visit a web site under attacker control. The issue only garners a 3.5 CVSS score, but yet it’s still fairly serious.

Thomas reported this issue responsibly to Google and they took it seriously. However, since then they have come back with a ridiculous remediation plan. Granted, its probably not entirely Google’s fault, but the overall situation looks very bleak for Android.

The problem is that Google stated that a fix will be available as part of an update to the upcoming Android 2.3. While that, in itself, may not be totally ridiculous, the reality of the situation is that Google is only one party involved in Android. There are two other groups, namely OEMs and Carriers, that must also do their part in getting the fix to users. Although Android devices are becoming increasingly functional, the security posture remains abysmal.

The security posture for desktop applications has improved vastly with all of the sand-boxing, automatic updates, and various other exploit mitigation technologies. Meanwhile, Android includes almost none of existing security protections. In fact, mobile users are being left out in the cold, unable to get a patch for a trivially exploitable cross-zone issue. For that matter, they can’t even control whether their device’s browser automatically downloads files or not.

This situation is not news, rather it is a sad fact. It is totally unfair for end users to be left out to fend for themselves. After all, they are paying a small fortune for these devices and the service to be able to use them. Hopefully the vendors involved will wake up before a network worm outbreak occurs.

Originally, Thomas disclosed the details of his bug on his blog. Later, he removed some details to help protect users. I believe that responsible disclosure is a two-way street that requires responsibility on both sides. Since Google, OEMs, and carriers all continue to act irresponsibly, it is necessary bring more attention to this issue and the situation as a whole.

I spent a little time and managed to recreate the issue with nothing more than HTML and JavaScript. As of today, I have released a Metasploit module to take advantage of the flaw. It is available in the latest copy of our Framework product, or you can view the source via the link to our Redmine project tracker above.

Before I go deeper into the consequence of this bug, I want to point out that Thomas outlined several workarounds for this vulnerability in his blog.

Now, take a deep breath give some thanks to the fact that, under Android, most every process runs under a separate, confined, unix-style user account. This design feature partially mitigates this issue, lowering confidentiality impact to “Partial" and bringing the CVSS score from 5 to 3.5. That said, an attacker can still gain access to some pretty interesting stuff.

For starters, an attacker can steal any world-readable file. In my tests it was possible to get potentially sensitive information from the within the “proc" file system. This type of information could include kernel versions, addresses, or configuration that can be used enhance further attacks.

Also, you can snarf any files that are used by the browser itself. This includes bookmarks, history, and likely more. This kind of information could potentially be embarrassing or possibly even give an attacker access to any saved passwords or session cookies you might have stored.

Perhaps the easiest win though, is that you can grab anything off of the SD card. You might ask, “Anything?! What about the user separation?" Well, because the SD card has been formatted with the “vfat" (aka “fat32") file system, there is no concept of ownership. All files are owned by the same user id since the file system itself cannot encapsulate who created which file. As Thomas said, files in the SD card that have predictable names are ripe for the picking. This includes pictures and movies. These may in fact be some of the most private data on your device.

In conclusion, I hope that the Android security debacle will get resolved as soon as possible. If Google, OEMs, and carriers can’t work it out, perhaps another party will step in to maintain the operating system. I believe this could be very similar to the way various Linux distributions operate today. If the situation is not resolved, I fear the Android device pool could become a seething cesspool of malicious code...

rapid7@sgaur.hosted.jivesoftware.com 19 Jan, 2011