CVE-2025-39824: debian debian_linux Use After Free

Vulnerability summary

CVE-2025-39824 is a high (CVSS 7.8) Use After Free vulnerability in debian debian_linux. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 5.5% of scored vulnerabilities.

Timeline

1. 16-09-2025
   PublishedVulnerability first disclosed.
2. 12-05-2026
   Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: HID: asus: fix UAF via HID_CLAIMED_INPUT validation After hid_hw_start() is called hidinput_connect() will eventually be called to set up the device with the input layer since the HID_CONNECT_DEFAULT connect mask is used. During hidinput_connect() all input and output reports are processed and corresponding hid_inputs are allocated and configured via hidinput_configure_usages(). This process involves slot tagging report fields and configuring usages by setting relevant bits in the capability bitmaps. However it is possible that the capability bitmaps are not set at all leading to the subsequent hidinput_has_been_populated() check to fail leading to the freeing of the hid_input and the underlying input device. This becomes problematic because a malicious HID device like a ASUS ROG N-Key keyboard can trigger the above scenario via a specially crafted descriptor which then leads to a user-after-free when the name of the freed input device is written to later on after hid_hw_start(). Below, report 93 intentionally utilises the HID_UP_UNDEFINED Usage Page which is skipped during usage configuration, leading to the frees. 0x05, 0x0D, // Usage Page (Digitizer) 0x09, 0x05, // Usage (Touch Pad) 0xA1, 0x01, // Collection (Application) 0x85, 0x0D, // Report ID (13) 0x06, 0x00, 0xFF, // Usage Page (Vendor Defined 0xFF00) 0x09, 0xC5, // Usage (0xC5) 0x15, 0x00, // Logical Minimum (0) 0x26, 0xFF, 0x00, // Logical Maximum (255) 0x75, 0x08, // Report Size (8) 0x95, 0x04, // Report Count (4) 0xB1, 0x02, // Feature (Data,Var,Abs) 0x85, 0x5D, // Report ID (93) 0x06, 0x00, 0x00, // Usage Page (Undefined) 0x09, 0x01, // Usage (0x01) 0x15, 0x00, // Logical Minimum (0) 0x26, 0xFF, 0x00, // Logical Maximum (255) 0x75, 0x08, // Report Size (8) 0x95, 0x1B, // Report Count (27) 0x81, 0x02, // Input (Data,Var,Abs) 0xC0, // End Collection Below is the KASAN splat after triggering the UAF: [ 21.672709] ================================================================== [ 21.673700] BUG: KASAN: slab-use-after-free in asus_probe+0xeeb/0xf80 [ 21.673700] Write of size 8 at addr ffff88810a0ac000 by task kworker/1:2/54 [ 21.673700] [ 21.673700] CPU: 1 UID: 0 PID: 54 Comm: kworker/1:2 Not tainted 6.16.0-rc4-g9773391cf4dd-dirty #36 PREEMPT(voluntary) [ 21.673700] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 [ 21.673700] Call Trace: [ 21.673700] <TASK> [ 21.673700] dump_stack_lvl+0x5f/0x80 [ 21.673700] print_report+0xd1/0x660 [ 21.673700] kasan_report+0xe5/0x120 [ 21.673700] __asan_report_store8_noabort+0x1b/0x30 [ 21.673700] asus_probe+0xeeb/0xf80 [ 21.673700] hid_device_probe+0x2ee/0x700 [ 21.673700] really_probe+0x1c6/0x6b0 [ 21.673700] __driver_probe_device+0x24f/0x310 [ 21.673700] driver_probe_device+0x4e/0x220 [...] [ 21.673700] [ 21.673700] Allocated by task 54: [ 21.673700] kasan_save_stack+0x3d/0x60 [ 21.673700] kasan_save_track+0x18/0x40 [ 21.673700] kasan_save_alloc_info+0x3b/0x50 [ 21.673700] __kasan_kmalloc+0x9c/0xa0 [ 21.673700] __kmalloc_cache_noprof+0x139/0x340 [ 21.673700] input_allocate_device+0x44/0x370 [ 21.673700] hidinput_connect+0xcb6/0x2630 [ 21.673700] hid_connect+0xf74/0x1d60 [ 21.673700] hid_hw_start+0x8c/0x110 [ 21.673700] asus_probe+0x5a3/0xf80 [ 21.673700] hid_device_probe+0x2ee/0x700 [ 21.673700] really_probe+0x1c6/0x6b0 [ 21.673700] __driver_probe_device+0x24f/0x310 [ 21.673700] driver_probe_device+0x4e/0x220 [...] [ 21.673700] [ 21.673700] Freed by task 54: [ 21.673700] kasan_save_stack+0x3d/0x60 [ 21.673700] kasan_save_track+0x18/0x40 [ 21.673700] kasan_save_free_info+0x3f/0x60 [ 21.673700] __kasan_slab_free+0x3c/0x50 [ 21.673700] kfre ---truncated---

• CWE-416Use After FreeThe product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.