CVE-2025-38494: Linux Kernel Privilege Escalation Flaw

CVE-2025-38494 Overview

CVE-2025-38494 is a Linux kernel vulnerability in the Human Interface Device (HID) core subsystem. The flaw allows low-level transport driver functions to be called directly, bypassing the validation performed by hid_hw_raw_request(). This wrapper normally ensures that the caller-provided buffer and length parameters are valid before they reach transport drivers. Skipping these checks permits invalid parameters to reach transport code paths, creating conditions that can lead to local privilege escalation or memory corruption on affected systems.

The issue affects mainline Linux kernel builds including 6.16 release candidates and downstream distributions such as Debian.

Critical Impact
A local, authenticated attacker with access to a HID transport interface can supply crafted buffers or lengths that reach transport driver code without validation, potentially compromising kernel confidentiality, integrity, and availability.

Affected Products

Linux kernel (multiple stable branches, including 6.16-rc1 through 6.16-rc6)
Debian GNU/Linux 11 (Bullseye)
Downstream distributions consuming affected stable kernel branches

Discovery Timeline

2025-07-28 - CVE-2025-38494 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-38494

Vulnerability Analysis

The Linux HID core provides hid_hw_raw_request() as the sanctioned entry point for submitting raw HID reports. The wrapper validates that the provided buffer pointer and the requested length are consistent with what the underlying transport can accept. Certain code paths in the kernel invoked the low-level transport driver callback directly instead of going through hid_hw_raw_request(). These direct calls skipped the parameter checks and allowed invalid buffer and length combinations to reach transport driver code.

When a transport driver receives an unchecked buffer or an oversized length, it can trigger out-of-bounds memory access or other memory safety violations inside the kernel. The fix restores use of hid_hw_raw_request() so all callers benefit from centralized validation.

Root Cause

The root cause is a missing input validation layer in HID call sites that bypassed the hid_hw_raw_request() helper. The helper enforces sanity checks on caller-supplied parameters. Direct invocation of the transport driver function removed those checks, allowing malformed requests to propagate into transport-specific handling logic.

Attack Vector

Exploitation requires local access with the ability to interact with a HID device interface, for example through a userspace driver, an ioctl path, or a privileged HID-related subsystem call. A crafted request with an invalid buffer or length can reach transport handling code and induce kernel memory corruption. Successful exploitation can lead to arbitrary kernel code execution or a denial-of-service condition affecting the host.

No public exploit code has been observed, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. See the kernel commit fixing the bypass for the authoritative technical description.

Detection Methods for CVE-2025-38494

Indicators of Compromise

Unexpected kernel oops, panic, or KASAN reports referencing HID transport driver functions such as usbhid or i2c-hid raw request paths.
Kernel logs containing memory access faults originating from HID report handling around the time an unprivileged process opened a /dev/hidraw* device.
Loading of untrusted out-of-tree HID drivers or unusual ioctl traffic against HID character devices.

Detection Strategies

Inventory running kernel versions across Linux fleets and flag any host running an affected 6.16-rc build or an unpatched stable branch referenced in the kernel.org commits.
Monitor dmesg and journalctl -k for HID-related warnings, WARN_ON traces, or KASAN slab-out-of-bounds messages in HID code paths.
Correlate process telemetry with access to HID device nodes to identify unusual local processes attempting raw HID report submission.

Monitoring Recommendations

Ingest kernel logs into a centralized logging or SIEM platform and alert on new kernel oops signatures referencing hid_ symbols.
Track package versions of linux-image-* on Debian systems and generate compliance alerts for hosts running kernels prior to the fixed Debian LTS release.
Baseline which users and services legitimately open HID devices, and alert on deviations from that baseline.

How to Mitigate CVE-2025-38494

Immediate Actions Required

Upgrade the Linux kernel to a version containing the fix from the referenced stable branch commits on kernel.org.
Apply the Debian LTS security updates published in the October 2025 advisories for affected Debian releases.
Restrict access to HID device nodes (/dev/hidraw*, /dev/uhid) to trusted users and services through file permissions and udev rules.

Patch Information

The fix restores the use of hid_hw_raw_request() so buffer and length validation cannot be bypassed. Patches are available across multiple stable branches via the kernel.org commits: 0e5017d8, 19d1314d, 40e25aa7, a62a895e, c2ca42f1, d18f63e8, dd8e8314, and f10923b8. Debian users should apply the updates announced in the Debian LTS advisory (msg00007) and Debian LTS advisory (msg00008).

Workarounds

Blacklist unused HID transport modules (for example, usbhid on systems that do not require HID input) using /etc/modprobe.d/ where operationally feasible.
Enforce tighter permissions on /dev/hidraw* and /dev/uhid so only privileged services can submit raw HID reports.
Where kernel updates cannot be applied immediately, reduce attack surface by disallowing untrusted local users and containers from accessing HID devices.

bash

# Verify running kernel and check for the HID fix on Debian
uname -r
apt list --installed 2>/dev/null | grep linux-image
apt-get update && apt-get install --only-upgrade linux-image-$(uname -r | sed 's/.*-//')

# Restrict access to raw HID devices
ls -l /dev/hidraw* /dev/uhid 2>/dev/null
chmod 0600 /dev/hidraw* /dev/uhid