Researchers have devised an attack that forces Apple’s Safari browser to divulge passwords, Gmail message content, and other secrets by exploiting a side channel vulnerability in the A- and M-series CPUs running modern iOS and macOS devices.
iLeakage, as the academic researchers have named the attack, is practical and requires minimal resources to carry out. It does, however, require extensive reverse-engineering of Apple hardware and significant expertise in exploiting a class of vulnerability known as a side channel, which leaks secrets based on clues left in electromagnetic emanations, data caches, or other manifestations of a targeted system. The side channel in this case is speculative execution, a performance enhancement feature found in modern CPUs that has formed the basis of a widecorpus of attacks in recent years. The nearly endless stream of exploit variants has left chip makers—primarily Intel and, to a lesser extent, AMD—scrambling to devise mitigations.
Exploiting WebKit on Apple silicon
The researchers implement iLeakage as a website. When visited by a vulnerable macOS or iOS device, the website uses JavaScript to surreptitiously open a separate website of the attacker’s choice and recover site content rendered in a pop-up window. The researchers have successfully leveraged iLeakage to recover YouTube viewing history, the content of a Gmail inbox—when a target is logged in—and a password as it’s being autofilled by a credential manager. Once visited, the iLeakage site requires about five minutes to profile the target machine and, on average, roughly another 30 seconds to extract a 512-bit secret, such as a 64-character string.
Enlarge/ Top: An email displayed in Gmail’s web view. Bottom: Recovered sender address, subject, and content.
Kim, et al.
“We show how an attacker can induce Safari to render an arbitrary webpage, subsequently recovering sensitive information present within it using speculative execution,” the researchers wrote on an informational website. “In particular, we demonstrate how Safari allows a malicious webpage to recover secrets from popular high-value targets, such as Gmail inbox content. Finally, we demonstrate the recovery of passwords, in case these are autofilled by credential managers.”
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For the attack to work, a vulnerable computer must first visit the iLeakage website. For attacks involving YouTube, Gmail, or any other specific Web property, a user should be logged into their account at the same time the attack site is open. And as noted earlier, the attacker website needs to spend about five minutes probing the visiting device. Then, using the window.open JavaScript method, iLeakage can cause the browser to open any other site and begin siphoning certain data at anywhere from 24 to 34 bits per second.
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iLeakage is a practical attack that requires only minimal physical resources to carry out. The biggest challenge—and it’s considerable—is the high caliber of technical expertise required. An attacker needs to not only have years of experience exploiting speculative execution vulnerabilities in general but also have fully reverse-engineered A- and M-series chips to gain insights into the side channel they contain. There’s no indication that this vulnerability has ever been discovered before, let alone actively exploited in the wild.
That means the chances of this vulnerability being used in real-world attacks anytime soon are slim, if not next to zero. It’s likely that Apple’s scheduled fix will be in place long before an iLeakage-style attack site does become viable.
