Decades-Old File Notification Flaws Expose Sensitive Data Across Major Operating Systems
Researchers have uncovered long-standing vulnerabilities in file notification systems on Android, Linux, macOS, and Windows, enabling unprivileged users to infer sensitive activities like keystrokes and website visits.
Security researchers from Austria's Graz University of Technology have identified fundamental flaws in the file notification subsystems of major operating systems, including Android, Linux, macOS, and Windows. These vulnerabilities, some dating back decades, allow unprivileged users to glean sensitive information about system and user activities through side-channel data leakage. The affected systems are Linux's inotify (since 2005), Android's FileObserver (since 2008), Windows' ReadDirectoryChangesW (since 2000), and macOS's FSEvents (since 2007).
These file notification subsystems are designed to alert applications when files are changed, opened, written, or deleted. While they do not expose file contents directly, the metadata and timing of these events can be exploited. Attackers can use this information to infer a wide range of activities, including keystrokes, website visits through fingerprinting, and even conduct UI redress attacks to steal credentials.
The researchers detailed their findings in a paper titled "File Notification Attacks: Templating and Exploiting Side-Channel Leakage from the File-Notification Systems on Linux, Windows, and macOS." The core issue lies in the accessibility of these notification subsystems to unprivileged users and, on some systems like Linux and Windows, the availability of file information even without explicit read permissions.
On Linux, the researchers demonstrated that watching a readable directory can leak events for files that the attacker cannot directly read. By monitoring the /dev/input directory, they achieved a high accuracy rate (93.1–100 percent) for inter-keystroke-timing attacks, both locally and remotely over SSH. They also successfully performed an authentication-prompt redress attack on KDE Plasma 6 under Wayland and website fingerprinting with 87.9 percent accuracy on the top 100 websites.
A partial fix for the Linux vulnerability, identified as CVE-2025-68788, was released in late 2025. This patch specifically prevents the generation of "access" and "modify" events on special files within the /dev/ directory. However, the broader implications of file notification leakage across the OS ecosystem remain.
For Android, the FileObserver mechanism bypasses the FUSE layer intended for per-app storage isolation. This allows a malicious app to monitor sensitive directories, such as WhatsApp's private folders, and infer when photos, documents, or messages are sent or received based on file names and timestamps.
Microsoft, when notified, reportedly described the behavior on Windows as "by-design" and an "undocumented feature." Despite this, the researchers found that watching the root C:\ directory on Windows could reveal the full path of every file accessed across the system, enabling real-time tracking of website visits in Firefox with 97.8 percent accuracy. Apple's macOS, while less susceptible to certain bypasses, still allowed monitoring of various file changes that could reveal system activities.
The researchers advocate for more robust mitigations, including extending capability checks to prevent monitoring of one's own files and any readable file. They propose specific solutions such as disallowing the monitoring of entire drives on Windows and implementing a permission system for file monitoring on Windows and macOS. The findings are scheduled to be presented at ACM CCS 2026.