Security researchers affiliated with Graz University of Technology have identified flaws in the file-notification systems of Android, Linux, macOS, and Windows that can expose sensitive information about users’ activities.
Sudheendra Raghav Neela, a doctoral student at TU Graz, said the vulnerabilities stem from file-notification subsystems included in modern operating systems to alert applications when files change. “We found decades-old bugs on these operating systems,” he told The Register.
The affected technologies include inotify on Linux, introduced in 2005; FileObserver on Android, introduced in 2008; ReadDirectoryChangesW on Windows, introduced in 2000; and FSEvents on macOS, introduced in 2007.
These subsystems report when a file is opened, changed, written, or deleted. They do not expose the contents of files, but the resulting event data can serve as a side channel through which a malicious user may infer what other people are doing on a computer.
Depending on the system and its configuration, an attacker could use this information for inter-keystroke-timing attacks to reconstruct user input, including remotely over SSH; website fingerprinting to identify sites being visited; and UI redress attacks designed to steal credentials.
Neela and his colleagues—Xufan Zhao, Jeanette Angelika Wultsch, Hannes Weissteiner, Florian Draschbacher, Stefan Gast, and Daniel Gruss—describe the findings in a paper titled “File Notification Attacks: Templating and Exploiting Side-Channel Leakage from the File-Notification Systems on Linux, Windows, and macOS.” Their research is summarized at inoti.fyi.
The core problem is that unprivileged users can access file-notification services. On Linux and Windows, file information may be available even when the user has no permission to read the underlying file. Although the most practical attack scenarios involve a local user targeting readable files shared with other accounts, the researchers warn that many globally readable files exist.
“On Linux, watching a readable directory leaks events on files inside it you cannot even read,” Neela said. “Watching /dev/input gives a notification on every keystroke, which we turn into a local inter-keystroke timing attack with a 93.1–100 percent [keystroke accuracy] score across seven users and a remote (SSH) one at 100 percent.”
The team also demonstrated an authentication-prompt redress attack against KDE Plasma 6 under Wayland and achieved 87.9 percent accuracy in website fingerprinting tests covering the 100 most visited sites.
The Linux vulnerability, identified as CVE-2025-68788, was partly addressed in December 2025 in kernel versions 5.10.248, 5.15.198, 6.1.160, 6.6.120, 6.12.64, and 6.18.3. The patch stops special files in /dev/ from generating “access” and “modify” events.
On Android, FileObserver extends beyond the FUSE layer intended to isolate each app’s storage. As a result, an app without special permissions may monitor another app’s private directory and identify files by name and timestamp. Neela cited WhatsApp’s private folder, where file events could reveal when photos, videos, and documents are sent, received, or deleted.
The researchers said they disclosed their findings responsibly to the relevant security teams between August and October 2025. However, they found no Android mitigation. Apple’s macOS provided the least exposure because the team found no way to bypass permissions for private directories, although FSEvents still exposed numerous file changes recorded in .plist files. These included audio input and output changes, power-setting updates, Bluetooth-device and printer activity, DNS changes triggered by network connections, and volume-mount or unmount events. Installing and removing applications could also be observed.
On Windows, monitoring the C:\ root directory exposes the full path of every file touched anywhere on the system, across all users and regardless of permissions. Neela said this information was sufficient to track another user’s Firefox activity in real time with 97.8 percent accuracy.
“Microsoft told us this is ‘by-design’ and that it’s an undocumented feature,” Neela said. The company’s response was subsequently nominated for the lamest vendor response at the Pwnie Awards 2026.
The researchers argue that file-notification attacks affect every major operating system and require broader safeguards. Although protections for device files have begun to appear, they say capability checks should also apply when monitoring a user’s own files and any file that user can read.
“On Windows, we propose disallowing the monitoring of entire drives,” the authors write. “On Windows and macOS, the kernel could introduce a permission system (for context, access control, owned files and directories, minifilters).”
The paper is scheduled to be presented at ACM CCS 2026 in The Hague, Netherlands, in November.
