The Linux kernel's touchwin input driver accumulates serial bytes into a fixed three-byte buffer with an index reset only when a full packet is received and the device-controlled second and third bytes match. A malicious or counterfeit Touchwindow peripheral can send non-zero bytes with differing second and third bytes, preventing the index reset and causing the index to exceed the buffer length. This results in an unbounded heap out-of-bounds write, allowing an attacker to overwrite adjacent heap memory one byte at a time. The fix involves resetting the packet index on every completed packet and only reporting events when the two bytes match, aligning with other serio touchscreen drivers.

An attacker controlling a malicious or malfunctioning Touchwindow device can exploit this vulnerability to perform unbounded heap out-of-bounds writes in kernel memory. This could lead to memory corruption, potential privilege escalation, or system instability. However, exploitation requires physical or logical control over the input device, limiting the attack vector.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The described fix resets the packet index on every completed packet and reports events only when the two Y bytes match, preventing the out-of-bounds write. Users should monitor for official Linux kernel updates addressing CVE-2026-64271 and apply them promptly once available.