CVE-2026-63908 Overview
CVE-2026-63908 is an off-by-one boundary check vulnerability in the Linux kernel's atmel_mxt_ts touchscreen driver. The flaw resides in the mxt_prepare_cfg_mem function, which parses configuration files supplied to the driver. When a configuration file declares an object size larger than the driver's expected mxt_obj_size(object), an incorrect comparison allows one extra byte to be written past the intended object boundary. This results in a one-byte out-of-bounds write into an adjacent object or instance in kernel memory.
Critical Impact
A malformed configuration file processed by the atmel_mxt_ts driver can corrupt adjacent kernel memory, potentially leading to memory corruption, driver instability, or local privilege escalation on affected systems.
Affected Products
- Linux kernel builds including the atmel_mxt_ts Atmel maXTouch touchscreen driver
- Distributions shipping vulnerable stable kernel branches prior to the referenced fix commits
- Embedded and mobile Linux systems using Atmel maXTouch controllers
Discovery Timeline
- 2026-07-19 - CVE-2026-63908 published to NVD
- 2026-07-19 - Last updated in NVD database
Technical Details for CVE-2026-63908
Vulnerability Analysis
The vulnerability is a classic off-by-one boundary error [CWE-193] resulting in a single-byte out-of-bounds write [CWE-787]. The mxt_prepare_cfg_mem function iterates over configuration bytes using a loop of the form for (i = 0; i < size; i++). Inside the loop, extra bytes beyond the driver's known object size were skipped using the check if (i > mxt_obj_size(object)) continue;. Because i is a zero-based index, valid indices span 0 through mxt_obj_size(object) - 1. When i equals mxt_obj_size(object), the condition evaluates to false and the byte is processed instead of discarded. The driver then computes byte_offset = reg + i - cfg->start_ofs and writes the byte, overwriting one byte of the adjacent instance or object in the mapped configuration memory. The fix changes the comparison to >=, ensuring the exact boundary index is also skipped.
Root Cause
The root cause is an incorrect relational operator in a boundary check. Using strict greater-than instead of greater-than-or-equal against a zero-based loop index allowed the terminal index to bypass the sanity check. This is a classic input validation and boundary condition error.
Attack Vector
Exploitation requires the kernel to load a crafted configuration blob for the atmel_mxt_ts device, which typically originates from firmware or a userspace-supplied configuration file. An attacker able to influence the configuration data delivered to the driver can trigger a controlled one-byte overwrite of adjacent driver state. The corruption is bounded to a single byte per malformed object, but repeated triggers or targeted layouts may enable further memory corruption.
No verified public exploit code is available. See the referenced kernel stable commits for the fix implementation.
Detection Methods for CVE-2026-63908
Indicators of Compromise
- Unexpected kernel warnings, oopses, or KASAN slab-out-of-bounds reports referencing mxt_prepare_cfg_mem or atmel_mxt_ts
- Touchscreen or input subsystem instability following configuration reloads on systems using Atmel maXTouch controllers
- Loading of non-standard or attacker-supplied maXTouch configuration files via sysfs update interfaces
Detection Strategies
- Enable CONFIG_KASAN on test kernels to catch the one-byte out-of-bounds write at runtime
- Audit installed kernel versions against the fixed stable commits listed in the NVD references
- Monitor dmesg and journal logs for atmel_mxt_ts error messages during configuration updates
Monitoring Recommendations
- Track kernel package versions across the fleet and flag hosts running unpatched stable branches
- Alert on write access to maXTouch update_cfg sysfs entries from unexpected userspace processes
- Collect kernel crash telemetry centrally to correlate driver faults with configuration-loading events
How to Mitigate CVE-2026-63908
Immediate Actions Required
- Apply vendor kernel updates that include the corrected >= boundary check in mxt_prepare_cfg_mem
- Restrict which users and processes can write maXTouch configuration files or trigger firmware reloads
- Validate the integrity and provenance of any configuration blobs delivered to the atmel_mxt_ts driver
Patch Information
The upstream fix updates the boundary check from if (i > mxt_obj_size(object)) to if (i >= mxt_obj_size(object)) so that the terminal index is correctly skipped. Patches have been backported across multiple stable branches. Reference the following commits: 1017e1c6, 5c3681c3, 6c6b989b, 7f95f479, 862a1a32, ae92e334, baa0210f, and e9b62996.
Workarounds
- Unload the atmel_mxt_ts module on systems that do not require Atmel maXTouch input hardware
- Remove write permissions to the maXTouch configuration update sysfs endpoints for non-root users
- Ship only trusted, validated configuration files with known-good object sizes to affected devices
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
