Security Experts:

Apple Adds 'BlastDoor' to Secure iPhones From Zero-Click Attacks

Apple has quietly added several anti-exploit mitigations into its flagship mobile operating system in what appears to be a specific response to zero-click iMessage attacks observed in the wild.

The new mitigations were discovered by Samuel Groß, a Google Project Zero security researcher who specializes in remote iPhone exploitation and zero-click attacks against mobile messaging systems.

Apple did not document the changes but Groß said he fiddled around with the newest iOS 14 and found that Apple shipped a “significant refactoring of iMessage processing” that severely cripples the usual ways exploits are chained together for zero-click attacks.

Groß notes that memory corruption based zero-click exploits typically require exploitation of multiple vulnerabilities to create exploit chains.  In most observed attacks, these could include a memory corruption vulnerability, reachable without user interaction and ideally without triggering any user notifications; a way to break ASLR remotely; a way to turn the vulnerability into remote code execution;; and a way to break out of any sandbox, typically by exploiting a separate vulnerability in another operating system component (e.g. a userspace service or the kernel).

With iOS 14, Groß discovered that Apple shipped a significant refactoring of iMessage processing, and made all four parts of an attack much harder to succeed. 

The first big addition is a new, tightly sandboxed “BlastDoor” service that is now responsible for the parsing of untrusted data in iMessages.

Separately, Apple added logic into iOS 14 to specifically detect [shared cache region] attacks and new techniques to limit an attacker’s ability to retry exploits or brute force Address Space Layout Randomization (ASLR).

The mitigations, Groß said, made all four parts of a typical zero-click attack harder and he commended Apple for responding to the work of offense-focused hackers to respond to documented in-the-wild attacks.

“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,” the Google researcher added.

Related: iOS Exploit Allows 'Unfettered Access' to iPhone User Data Over Wi-Fi

RelatedGoogle Researchers Detail Critical iMessage Vulnerability

Related: Apple Ships Emergency Fixes for Under-Attack iOS Zero-Day

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Ryan Naraine is Editor-at-Large at SecurityWeek and host of the popular Security Conversations podcast series. He is a journalist and cybersecurity strategist with more than 20 years experience covering IT security and technology trends. Ryan has built security engagement programs at major global brands, including Intel Corp., Bishop Fox and Kaspersky GReAT. He is a co-founder of Threatpost and the global SAS conference series. Ryan's career as a journalist includes bylines at major technology publications including Ziff Davis eWEEK, CBS Interactive's ZDNet, PCMag and PC World. Ryan is a director of the Security Tinkerers non-profit, and a regular speaker at security conferences around the world. Follow Ryan on Twitter @ryanaraine.