Late last week a new jailbreak method was released for iOS 4 and iPhone OS 3.x based devices such as the iPhone, iPod, and iPad. Jailbreaking these devices is nothing new. It's been done for years to allow these devises to run applications not approved by Apple, and also as a means to unlock iPhones for use on other carriers. What is different in this new method is that all that it takes to jailbreak the device is to visit a specific website using the built-in Web browser. Previously users had to connect the device to a computer and use software for Windows or Mac to complete the process.
At jailbreakme.com, all it takes to complete the jailbreak is to slide the arrow to the right and wait for the process to complete. To perform the jailbreak the process takes advantage of two vulnerabilities; one in how Safari parses PDF files, and one in the kernel of iOS/iPhoneOS. VUPEN has more information about these vulnerabilities in their advisory.
Apple is reportedly looking into the vulnerability issues, but until they have issued a patch, all users of iPhones, iPads, or iPods are at risk, because there is nothing that prevents a malicious attacker from using these vulnerabilities to automatically install malware onto the device. Reports around the Web are claiming that there isn't much a user can do to prevent this type of attack unless you've already jailbroken, as there is an add-on, via Cydia, that will warn you for every PDF you open. However, this is not entirely true.
While it is true that Safari and other Web browsers on iOS/iPhoneOS automatically render and display a PDF page, and therefore will load the exploit automatically, some third-party browsers have customizable filters that can block the attack and prevent your device from compromise. Two examples are Atomic Web Browser and iCabMobile, both of which work on iPhone, iPod Touch, and iPad.
Here is how you enable and tweak the application filters to prevent PDFs from being downloaded in the browser.
Atomic Web Browser
- Start the application, click the Settings icon, and click Settings.
- Click "Ad Block Settings" and then "Edit Ad Block".
- Click "New Filter" and then enter: *.pdf
- Click "Done" and "Save".
- Click "Ad Block" at the top-left corner and enable the Ad Block Feature.
- Start the iCabMobile application and click the Settings icon.
- Scroll down until you see "Edit Filters" and click that selection.
- Click "Create New Filter" and enter: *.pdf
- Click "Done" and then "Tools" in the upper-left corner to go back to the Settings menu.
- Scroll up and make sure that the "Enable Filters" settings is set to "On".
While we at Websense, Inc. don't support or endorse these products, neither of which are free, they could be a worthwhile investment until Apple fixes the problem.
Finally, don't forget that these third-party browsers will not protect you if you get a PDF in an email message, click on a link in an email/SMS or click on a link that launches a built-in browser in the app (like Twitter, Facebook etc). These all use the Safari engine to view the PDF and will bypass the third-party browser filters.