CVE-2025-68777: Linux Kernel Buffer Overflow Vulnerability

CVE-2025-68777 Overview

An off-by-one error vulnerability has been identified in the Linux kernel's ti_am335x_tsc touchscreen driver. The flaw exists in the wire_order validation logic, where an improper boundary check allows array indices to equal the array size rather than being strictly less than it. This results in potential out-of-bounds memory access when the wire_order value is used as an index into the config_pins array.

Critical Impact

Systems running affected Linux kernel versions with the ti_am335x_tsc touchscreen controller driver may be vulnerable to out-of-bounds memory access, potentially leading to kernel memory corruption or system instability.

Affected Products

• Linux kernel with ti_am335x_tsc touchscreen driver enabled
• Texas Instruments AM335x platform-based devices
• Embedded systems utilizing the AM335x touchscreen controller

Discovery Timeline

• 2026-01-13 - CVE CVE-2025-68777 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-68777

Vulnerability Analysis

The vulnerability resides in the input validation logic within the ti_am335x_tsc touchscreen controller driver. The config_pins array contains 4 elements, making valid indices 0 through 3. However, the original validation check used a greater-than comparison (wire_order[i] > ARRAY_SIZE(config_pins)) instead of a greater-than-or-equal comparison. This subtle logic error allows wire_order[i] to have a value of 4, which when used as an array index, accesses memory beyond the bounds of the config_pins array.

This type of off-by-one error is a classic boundary condition vulnerability that can lead to reading or writing kernel memory at unintended locations. In the context of a kernel driver, such out-of-bounds access could potentially expose sensitive kernel data or corrupt adjacent memory structures.

Root Cause

The root cause is an improper boundary validation using the wrong comparison operator. The validation logic wire_order[i] > ARRAY_SIZE(config_pins) should have been wire_order[i] >= ARRAY_SIZE(config_pins) to properly restrict array index values to the valid range of 0 to 3. This is a common programming error when dealing with zero-indexed arrays where the maximum valid index is one less than the array size.

Attack Vector

The attack vector for this vulnerability involves providing malformed device tree configuration or input data that sets wire_order values equal to the array size (4). When the driver processes this configuration, it attempts to access config_pins[4], reading memory past the end of the array. While exploitation may require local access or specific device configurations, the vulnerability could potentially be triggered through malicious device tree overlays or specially crafted input on affected embedded systems.

The vulnerability manifests in the wire_order validation function where boundary checking fails to account for zero-indexed array access. When wire_order[i] equals ARRAY_SIZE(config_pins), the subsequent array access config_pins[wire_order[i]] reads memory beyond the allocated array bounds. The fix involves changing the comparison operator from > to >= to ensure all array accesses remain within valid bounds. See the kernel commit history for technical implementation details.

Detection Methods for CVE-2025-68777

Indicators of Compromise

• Kernel panic or oops messages referencing ti_am335x_tsc driver functions
• Unexpected system crashes on AM335x-based embedded devices
• Memory corruption artifacts in kernel logs related to touchscreen subsystem
• Unusual kernel memory access patterns in the input driver subsystem

Detection Strategies

• Monitor kernel logs for out-of-bounds access warnings or KASAN (Kernel Address Sanitizer) reports
• Audit device tree configurations for wire_order values greater than or equal to 4
• Deploy kernel debugging tools to track memory access violations in the input subsystem
• Use static analysis tools to identify similar off-by-one boundary conditions in kernel drivers

Monitoring Recommendations

• Enable kernel memory debugging options such as KASAN to detect out-of-bounds access attempts
• Implement system monitoring for unexpected driver crashes or kernel panics on affected platforms
• Review embedded device firmware for outdated Linux kernel versions
• Configure alerting for touchscreen driver-related kernel error messages

How to Mitigate CVE-2025-68777

Immediate Actions Required

• Update to a patched Linux kernel version that includes the boundary check fix
• Review system configurations on AM335x-based devices for potentially triggering values
• If updates are not immediately possible, consider disabling the ti_am335x_tsc driver if touchscreen functionality is not required
• Monitor affected systems for signs of exploitation or instability

Patch Information

The vulnerability has been addressed through multiple kernel commits that correct the boundary validation logic. The fix changes the comparison operator from > to >= in the wire_order validation check, ensuring array indices remain within the valid range of 0-3.

Relevant kernel patches are available:

• Kernel Commit 08c0b56
• Kernel Commit 248d3a73
• Kernel Commit 40e3042d
• Kernel Commit 84e4d354
• Kernel Commit bf95ec55

Workarounds

• Disable the ti_am335x_tsc module if touchscreen functionality is not required: modprobe -r ti_am335x_tsc
• Ensure device tree configurations do not specify wire_order values of 4 or higher
• Implement additional input validation at the device tree configuration level
• For production systems, apply kernel updates during the next maintenance window

# Configuration example
# Disable the vulnerable touchscreen driver if not needed
echo "blacklist ti_am335x_tsc" >> /etc/modprobe.d/blacklist-ti-tsc.conf

# Verify the module is not loaded
lsmod | grep ti_am335x_tsc

# For systems requiring the driver, update to a patched kernel version
# Check current kernel version
uname -r

# Update kernel packages (example for Debian-based systems)
apt update && apt upgrade linux-image-$(uname -r)