CVE-2025-39806: HID: multitouch: fix slab out-of-bounds access in mt_report_fixup()

Vulnerability summary

CVE-2025-39806 is a high (CVSS 8.8) Out-of-bounds Read vulnerability in debian debian_linux. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 14.9% of scored vulnerabilities.

Timeline

1. 16-09-2025
   PublishedVulnerability first disclosed.
2. 05-08-2026
   Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: HID: multitouch: fix slab out-of-bounds access in mt_report_fixup() A malicious HID device can trigger a slab out-of-bounds during mt_report_fixup() by passing in report descriptor smaller than 607 bytes. mt_report_fixup() attempts to patch byte offset 607 of the descriptor with 0x25 by first checking if byte offset 607 is 0x15 however it lacks bounds checks to verify if the descriptor is big enough before conducting this check. Fix this bug by ensuring the descriptor size is at least 608 bytes before accessing it. Below is the KASAN splat after the out of bounds access happens: [ 13.671954] ================================================================== [ 13.672667] BUG: KASAN: slab-out-of-bounds in mt_report_fixup+0x103/0x110 [ 13.673297] Read of size 1 at addr ffff888103df39df by task kworker/0:1/10 [ 13.673297] [ 13.673297] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.15.0-00005-gec5d573d83f4-dirty #3 [ 13.673297] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/04 [ 13.673297] Call Trace: [ 13.673297] <TASK> [ 13.673297] dump_stack_lvl+0x5f/0x80 [ 13.673297] print_report+0xd1/0x660 [ 13.673297] kasan_report+0xe5/0x120 [ 13.673297] __asan_report_load1_noabort+0x18/0x20 [ 13.673297] mt_report_fixup+0x103/0x110 [ 13.673297] hid_open_report+0x1ef/0x810 [ 13.673297] mt_probe+0x422/0x960 [ 13.673297] hid_device_probe+0x2e2/0x6f0 [ 13.673297] really_probe+0x1c6/0x6b0 [ 13.673297] __driver_probe_device+0x24f/0x310 [ 13.673297] driver_probe_device+0x4e/0x220 [ 13.673297] __device_attach_driver+0x169/0x320 [ 13.673297] bus_for_each_drv+0x11d/0x1b0 [ 13.673297] __device_attach+0x1b8/0x3e0 [ 13.673297] device_initial_probe+0x12/0x20 [ 13.673297] bus_probe_device+0x13d/0x180 [ 13.673297] device_add+0xe3a/0x1670 [ 13.673297] hid_add_device+0x31d/0xa40 [...]

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.