CVE-2026-74673 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
Input: evdev - fix information leak in evdev_pass_values()
In evdev_pass_values(), the input_event structure is allocated on the kernel stack and populated field-by-field. However, it is never fully initialized. On architectures where struct input_event contains explicit or implicit padding (such as the 32-bit __pad field on SPARC64), these padding bytes are left uninitialized.
When this event structure is subsequently passed to the client buffer and later copied to userspace, the uninitialized padding bytes leak kernel stack memory, potentially exposing sensitive information.
Similar issues exist in __evdev_queue_syn_dropped and __pass_event.
Fix this by explicitly zeroing the entire event structure with memset() before populating its fields. This ensures all padding bytes are cleared before the data crosses the security boundary.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel input subsystem contains a critical information disclosure vulnerability within the evdev interface, specifically affecting functions such as evdev_pass_values(), __evdev_queue_syn_dropped, and __pass_event. These functions are responsible for processing input events from hardware devices and delivering them to user-space applications via event buffers. The core technical flaw lies in how the kernel prepares the input_event structure before transmission. In these routines, an instance of struct input_event is allocated on the kernel stack and populated field-by-field with data derived from device inputs or internal state. However, the code fails to fully initialize this structure prior to use. On certain architectures, particularly SPARC64 but potentially others depending on compiler padding rules, the input_event structure contains explicit or implicit padding bytes designed for memory alignment purposes. Because these padding regions are not explicitly zeroed out before being copied to userspace, they retain whatever data previously existed in that stack location.
This oversight results in a kernel information leak where uninitialized stack memory is exposed to unprivileged user-space processes. When the evdev interface copies the event structure into its buffer for delivery to clients, it includes these padding bytes as part of the payload. Since the kernel does not clear this memory before transmission, sensitive data from previous kernel operations that utilized the same stack space can be inadvertently disclosed. This type of vulnerability falls under CWE-200: Information Exposure and is categorized by MITRE ATT&CK as T1083: File and Directory Discovery or more broadly as part of Kernel Memory Disclosure techniques used to gather intelligence about system state, loaded modules, or cryptographic keys that may reside in kernel memory. The impact ranges from minor data leakage to potential exploitation aids for further attacks against the host system.
The resolution involves explicitly zeroing the entire event structure using memset() before any fields are populated with actual input data. This ensures that all padding bytes and unused portions of the struct are cleared, preventing stale stack contents from being transmitted across the security boundary between kernel space and user space. To mitigate this risk in environments where patching may not be immediately feasible, administrators should restrict access to evdev devices by ensuring proper file permissions on /dev/input/event* nodes. Limiting read/write access to only necessary users or services reduces the attack surface for exploitation of this information leak vulnerability.