iOS 14 rolls out ‘BlastDoor,’ a new sandbox security system

Users with iOS 14 are equipped with a new “BlastDoor” sandbox security system for their devices. The feature prevents attacks from the Messages app. Samuel Groß, a security researcher with Google’s Project Zero, discussed the new feature in his Project Zero blog post.

He explains a tightly sandboxed service is responsible for parsing all of the untrusted data in iMessages. It is responsible to execute code separately from the OS in isolation. The feature looks over the incoming messages, inspects their content in a secure environment, which prevents any malicious code inside of a message from interacting with iOS or accessing user data.

As can be seen, the majority of the processing of complex, untrusted data has been moved into the new BlastDoor service. Furthermore, this design with its 7+ involved services allows fine-grained sandboxing rules to be applied, for example, only the IMTransferAgent and apsd processes are required to perform network operations. As such, all services in this pipeline are now properly sandboxed (with the BlastDoor service arguably being sandboxed the strongest).

Over the past years, Security researchers have found iMessage remote code execution bugs that allow an iPhone to be sneaked into with just a text. The latest of these attacks took place last year which targeted Al Jazeera staffers and journalists.

According to Groß:

This blog post discussed three improvements in ‌iOS 14‌ affecting iMessage security: the BlastDoor service, resliding of the shared cache, and exponential throttling. Overall, these changes are probably very close to the best that could’ve been done given the need for backwards compatibility, and they should have a significant impact on the security of iMessage and the platform as a whole.

It’s great to see Apple putting aside the resources for these kinds of large refactorings to improve end users’ security. Furthermore, these changes also highlight the value of offensive security work: not just single bugs were fixed, but instead structural improvements were made based on insights gained from exploit development work.

While investigating a Messages hacking campaign that targeted Al Jazeera journalists, Groß found the new ‌iOS 14‌ feature. Here is the full Project Zero blog post.