Researchers at Graz University of Technology have disclosed a browser-based attack called FROST that can infer which websites a user visits and which apps they open by measuring SSD timing, with reported identification accuracy reaching 88.95% for the top 50 websites in a closed-world test on macOS.
KEY FACTS
- Attack method FROST uses JavaScript in a browser to watch for SSD contention in the background.
- Access path It relies on the Origin Private File System, a browser storage feature that does not trigger a permission prompt.
- Results The report says the attack reached 95.83% accuracy for ten pre-installed macOS apps.
- Scope The timing channel works on macOS and Linux, but the full classifier results were tested on macOS only.
The technical analysis from Graz University of Technology says the attack works inside the browser sandbox and needs no native code, extension or permission prompt. The page creates a file larger than available memory, then reads random 4 kB chunks in a loop and times each read with performance.now().
The report says the Origin Private File System, or OPFS, lets a site write to disk without asking the user first. On Chrome and Safari, OPFS can grow to 60% of disk space, while Firefox caps each origin lower. The researchers said an attacker can spread the load across multiple origins on Firefox.
According to the disclosure, cross-origin isolation can restore timer precision that browsers normally blunt. When a user opens another site or launches an app on the same drive, the resulting disk activity changes the timing trace. A neural network then classifies the trace.
The team also reported a covert channel using the same signal, with data rates of 661.63 bit/s on Linux and 719.27 bit/s on macOS through OPFS. The same group previously described the SnailLoad attack, which inferred sites and videos from network latency alone.
WHY IT MATTERS
The findings show that a normal website can learn about activity on the same disk without special software or user approval. The practical risk is strongest on single-drive systems, while the report says closing the tab stops the attack and that browser makers have not yet shipped a fix.