CVE-2025-68797: Linux Kernel NULL Pointer Vulnerability

CVE-2025-68797 Overview

A NULL pointer dereference vulnerability has been identified in the Linux kernel's Applicom character device driver. The vulnerability exists in the ac_ioctl function where improper validation of the IndexCard parameter and RamIO pointer occurs when the command value is 6. This flaw allows the function to unconditionally execute a readb operation on a potentially NULL pointer, leading to a kernel crash.

Critical Impact
Local attackers with access to the Applicom device interface can trigger a kernel NULL pointer dereference, causing a denial of service condition through system crash.

Affected Products

Linux kernel with Applicom character device driver (char/applicom.c)
Systems utilizing Applicom industrial communication boards
Multiple Linux kernel versions (patches available across stable branches)

Discovery Timeline

2026-01-13 - CVE CVE-2025-68797 published to NVD
2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-68797

Vulnerability Analysis

The vulnerability resides in the ac_ioctl function within the Applicom character device driver (drivers/char/applicom.c). The function handles various ioctl commands for interacting with Applicom industrial communication boards. When processing commands, the function typically validates the IndexCard parameter and verifies that the corresponding RamIO pointer in the apbs array is valid (non-NULL).

However, when the command (cmd) equals 6, this validation logic is bypassed entirely. The command value 6 represents a global information query that doesn't require targeting a specific board context. Despite this, the function unconditionally executes readb(apbs[IndexCard].RamIO + VERS) at the end of its execution path, regardless of the command type.

This creates a dangerous condition where an attacker can craft an ioctl call with cmd set to 6 and an IndexCard value referencing a non-existent or uninitialized board entry. Since validation is skipped for this command, the RamIO pointer may be NULL, and the subsequent readb operation will dereference a NULL pointer, triggering a kernel panic.

Root Cause

The root cause is an incomplete control flow design in the ac_ioctl function. The developers correctly identified that command 6 is a global query not requiring board-specific validation, but failed to account for the unconditional readb operation at the function's end. The fix involves adding a conditional check to skip the readb access when cmd is 6, properly isolating the global query path from board-specific memory operations.

Attack Vector

The attack vector requires local access to the system with permissions to interact with the Applicom device interface. An attacker would need to:

Open the Applicom device file (typically /dev/applicom)
Issue an ioctl system call with the command parameter set to 6
Provide an IndexCard value pointing to an uninitialized board slot where RamIO is NULL

Upon execution, the kernel will attempt to read from a NULL address offset by the VERS constant, resulting in a NULL pointer dereference and subsequent kernel panic. This vulnerability is primarily a denial of service vector, as exploitation results in system unavailability rather than code execution or privilege escalation.

Detection Methods for CVE-2025-68797

Indicators of Compromise

Kernel panic logs indicating NULL pointer dereference in ac_ioctl or applicom.c
System crashes occurring during ioctl operations on /dev/applicom device
Repeated unexpected reboots on systems with Applicom drivers loaded
Kernel oops messages referencing the readb function call within the Applicom driver

Detection Strategies

Monitor kernel logs for NULL pointer dereference events originating from the applicom module
Implement system call auditing for ioctl operations targeting Applicom device files
Deploy kernel module integrity monitoring to detect unpatched driver versions
Use runtime kernel instrumentation to detect abnormal memory access patterns in character device drivers

Monitoring Recommendations

Enable kernel crash dump collection to capture detailed information on any NULL pointer dereference events
Configure alerting for system stability anomalies on hosts with Applicom hardware or drivers
Implement centralized log aggregation for kernel messages across affected infrastructure
Monitor for suspicious process behavior involving repeated ioctl calls to character devices

How to Mitigate CVE-2025-68797

Immediate Actions Required

Apply the kernel patches from the stable branches immediately on affected systems
If patching is not immediately possible, consider unloading the applicom kernel module if Applicom hardware is not in use
Restrict access to the Applicom device files using filesystem permissions or SELinux/AppArmor policies
Monitor systems for crash events indicating potential exploitation attempts

Patch Information

The Linux kernel maintainers have released patches across multiple stable branches to address this vulnerability. The fix modifies the ac_ioctl function to skip the readb access when the command is 6, recognizing that this command is a global information query that does not require board-specific memory operations.

Patches are available at the following kernel git commits:

Workarounds

Unload the applicom kernel module if Applicom hardware is not required: modprobe -r applicom
Blacklist the module from loading at boot by adding blacklist applicom to /etc/modprobe.d/blacklist.conf
Restrict device file access permissions to limit who can interact with the Applicom driver
Use mandatory access control policies (SELinux, AppArmor) to confine processes that may interact with the device

bash

# Disable Applicom module loading
echo "blacklist applicom" >> /etc/modprobe.d/blacklist-applicom.conf
# Remove module if currently loaded
modprobe -r applicom
# Update initramfs to persist changes
update-initramfs -u