CVE-2026-23349: Linux Kernel HID pidff Vulnerability

CVE-2026-23349 Overview

A null pointer dereference vulnerability has been identified in the Linux kernel's HID (Human Interface Device) subsystem, specifically within the pidff (PID Force Feedback) driver. The vulnerability occurs due to improper clearing of conditional effect bits in the ffbit structure, which can lead to NULL pointer dereferences when handling force feedback effects.

Critical Impact

This vulnerability can cause kernel crashes and system instability when processing force feedback effects on HID devices, potentially leading to denial of service conditions on affected Linux systems.

Affected Products

• Linux kernel (versions with vulnerable HID pidff driver)

Discovery Timeline

• 2026-03-25 - CVE CVE-2026-23349 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-23349

Vulnerability Analysis

This vulnerability resides in the Linux kernel's HID pidff driver, which handles force feedback effects for input devices such as gaming controllers, joysticks, and steering wheels. The core issue stems from incomplete bit clearing operations when managing conditional effects within the force feedback subsystem.

When the driver processes conditional effects (such as spring, friction, damper, and inertia effects), it must properly manage a bitmap (ffbit) that tracks which effects are currently active or available. The vulnerable code fails to clear all conditional effect bits from this bitmap, leaving stale pointers that can subsequently be dereferenced as NULL when the driver attempts to access effect structures that no longer exist.

The vulnerability manifests during normal force feedback operations, particularly when effects are being removed or reconfigured. An attacker with local access could potentially trigger this condition by manipulating force feedback effect configurations through the device interface.

Root Cause

The root cause of this vulnerability is incomplete bit manipulation in the ffbit structure within the pidff driver. When conditional effects are cleared or removed, the driver was not properly clearing all associated bits from the effect bitmap. This leaves the driver in an inconsistent state where it believes certain effects exist (based on the bitmap) but the underlying data structures have been freed or were never properly initialized, resulting in NULL pointer dereferences when these phantom effects are accessed.

Attack Vector

The attack vector requires local access to a system with HID force feedback devices. An attacker would need to:

1. Have access to force feedback device interfaces (typically /dev/input/eventX)
2. Send specially crafted force feedback effect configurations
3. Trigger the condition where incomplete bit clearing leads to NULL pointer access

While exploitation requires local access and specific hardware conditions, successful exploitation results in kernel panic or system crash, causing denial of service.

The vulnerability mechanism involves improper state management in the force feedback subsystem. When conditional effects are manipulated, the incomplete clearing of ffbit entries leaves dangling references that cause NULL pointer dereferences upon subsequent access. For detailed technical analysis, refer to the kernel git commits.

Detection Methods for CVE-2026-23349

Indicators of Compromise

• Kernel panic or oops messages referencing the pidff module or HID force feedback functions
• System crashes occurring during force feedback device operations
• Kernel logs showing NULL pointer dereference errors in HID subsystem context

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for NULL pointer dereference errors related to HID or force feedback drivers
• Implement kernel crash dump analysis to identify crashes originating from the pidff driver
• Deploy system stability monitoring to detect unexpected reboots or kernel panics on systems with HID force feedback hardware

Monitoring Recommendations

• Enable kernel crash dump collection (kdump) to capture and analyze crashes for this vulnerability
• Set up alerting for kernel oops messages containing pidff, hid, or ff_effects in the call trace
• Monitor systems with gaming controllers, joysticks, or steering wheels for unusual stability issues

How to Mitigate CVE-2026-23349

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the fix for conditional effect bit clearing
• On systems where immediate patching is not possible, consider unloading or blacklisting the pidff module if force feedback functionality is not required
• Restrict access to force feedback device interfaces to trusted users only

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix properly clears all conditional effect bits from ffbit to prevent NULL pointer dereferences. The following commits contain the fix:

• Commit 97d5c8f5c09a
• Commit d1edc027a4b0
• Commit ef0e669dbcea

Apply the appropriate patch for your kernel version from upstream or your distribution's security updates.

Workarounds

• Blacklist the pidff module by adding blacklist pidff to /etc/modprobe.d/blacklist.conf if force feedback is not needed
• Restrict device permissions on /dev/input/event* to limit access to force feedback interfaces
• On production servers without HID force feedback requirements, disable the driver entirely at the kernel configuration level

# Configuration example
# Blacklist the pidff module to prevent loading
echo "blacklist pidff" | sudo tee /etc/modprobe.d/blacklist-pidff.conf

# Unload the module if currently loaded
sudo modprobe -r pidff

# Verify module is not loaded
lsmod | grep pidff