Websites have a new way to spy on visitors: analyzing their SSD activity

Sandboxed file systems isolate websites from each other and from device internals, but JavaScript can still measure I/O interactions. An attacker can repeatedly perform random reads from a very large OPFS file to observe SSD contention caused by user activity. These contention effects create measurable latency differences in the read operations. The attacker then trains a convolutional neural network on collected latency traces and uses the trained model to classify new traces, deducing which apps and websites are open. The approach requires an extremely large OPFS file, likely gigabytes, and the file must reside on the same SSD as the user. Closing unused tabs and limiting OPFS file sizes can reduce the side channel. No real-world attacks have been reported.

"“The attacker continuously measures SSD contention by performing random reads from a large OPFS file,” the researchers explained. “SSD contention caused by user activity causes measurable latency differences for these read operations. By training a convolutional neural network (CNN) on these traces, the attacker can fingerprint user activity on the host system by classifying new traces using the trained model.”"

"The technique has its limitations. First, the OPFS file must be extremely large-likely a gigabyte or more. That requirement means that attacks at scale would inevitably be detected by many users. Additionally, the OPFS file must be stored on the same SSD the visitor is using. This isn't usually a problem for tracking open websites, since the OPFS file is stored in the browser's default location. In the event apps are using a separate SSD drive for apps, those apps couldn't be detected by FROST."

"One of the best ways to prevent FROST attacks is to close tabs as soon as they're no longer needed. More savvy users can monitor the creation and size of OPFS files allocated by unknown websites. The researchers proposed ways for browser makers to shut down the side channel. One such method is to limit the maximum size such files that are allowed. There are no indications FROST attacks have been performed in the wild."

"The researchers performed the full Frost attack on an M2 Mac. On Linux, they showed that the underlying primitive (measuring SSD access latency traces from JavaScript) works, but didn't run the full attack."

Read at Ars Technica