A research team from Graz University of Technology in Austria has shown that a routine feature built into virtually every major operating system can be turned into a surveillance channel that tracks keystrokes, visited websites, and private messaging activity without needing administrator access.
The feature is the file-change notification system. Every major platform ships one: Linux has inotify and fanotify, Windows uses ReadDirectoryChangesW, and Android and macOS have their own equivalents. Text editors, antivirus software, cloud sync clients, and file managers depend on these APIs to react when files are created, modified, or deleted. The catch is that subscribing to those notifications requires no special privileges, only read access to the directory being watched.
What these APIs never hand over is actual file content. What they do leak, the researchers found, is file names and the exact timing of events. That combination is enough to reconstruct meaningful details about what other users on the same machine are doing throughout the day.
Linux: Keystrokes Through the Filesystem
On Linux, if a process is blocked from watching a specific file directly, it can still receive that file's events by watching the parent directory, as long as that directory is readable. The researchers applied this to device files under /dev that represent keyboard hardware. The result is that an unprivileged process can detect every keystroke another user makes, though not which key was pressed.
That gap offers less protection than it appears to. Research going back more than two decades has established that the rhythm of inter-keystroke timing can help reconstruct what was typed. In tests with seven participants, the attack scored between 93.1% and 100% on standard accuracy measures. Input that never echoes to the screen, such as a password entered during a sudo prompt, does not generate filesystem events and stays invisible to the attack.
The team also demonstrated website fingerprinting by watching which system fonts Firefox loads for a given page. Against the top 100 sites, that technique reached 87.9% accuracy. A third Linux attack targeted KDE Plasma 6 on Wayland: a malicious process running as the victim can detect when a real authentication dialog is about to appear and draw a counterfeit one over it to capture credentials before the legitimate prompt ever loads.
Android: No Permissions Required
On Android, an application requesting zero permissions can watch the private storage directory of a completely separate app. Testing against WhatsApp on a Google Pixel and a Samsung Galaxy device, the researchers extracted file names and event timing that revealed when photos, videos, and documents were sent or received. The attack also exposed when that media was later deleted, offering a window into communication patterns that the app's own privacy controls do not address.
Windows: One Watch, Every User's Files
The most consequential Windows scenario arises when a process watches the root of the system drive. Windows reports the full path of every file that changes anywhere on the machine, including paths inside other users' home directories that the monitoring account has no direct permission to access.
Because Firefox names profile subdirectories after associated websites, an unprivileged user watching the drive root can track which sites another logged-in account is browsing in near-real time. Across the top 1,000 websites, the researchers hit 97.8% accuracy against Firefox and 48.5% against Edge, which creates far fewer site-named folders.
This behavior comes from the same ReadDirectoryChangesW API that was flagged under CVE-2007-0843 for a similar class of issue almost two decades ago. Microsoft's position has not shifted. The company told the researchers the behavior is working as designed, on the grounds that file contents remain inaccessible. A Microsoft spokesperson told SecurityWeek that "the technique requires an attacker to already have the ability to run code locally on a device under a separate user account and does not provide access to file contents." Microsoft did note that administrators can enable optional protections it documented in April 2025 covering some path-disclosure scenarios tied to directory change notifications.
macOS came out the least exposed of the four platforms. Its equivalent API can only monitor globally readable files, which limits the attack surface, though the researchers still demonstrated tracking of application launches, app interactions, and settings changes.
The Linux kernel received a targeted patch under CVE-2025-68788, which stops the fsnotify subsystem from generating access and modify events for special files, including the device files representing keyboard input. The researchers describe this as addressing the most serious Linux issue, but other attack paths from their research remain open.
Apple and Google have not responded to requests for comment, and no fixes have been announced
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