The Linux kernel driver for hynitron_cstxxx incorrectly allows a finger identifier equal to or greater than the configured maximum touch slot count to be processed. Because the driver indexes into a fixed‑size report buffer without validating the touch count or finger ID, an out‑of‑range value can corrupt the state of a previously active touch slot. This leads to incorrect touch reporting and could result in a denial of service if the corrupted state affects higher‑level applications that rely on accurate touch input.

All Linux kernel installations that use the hynitron_cstxxx driver are affected, including the V821 Avaota F1 board which is configured with a single touch slot. Since finger ID 1 is already invalid on that device, any report containing an out‑of‑range ID will trigger the flaw.

The vulnerability is a classic input validation flaw (CWE‑20). No EPSS score is available and the flaw is not listed in CISA KEV, so its exploitation probability is currently unknown. The likely attack vector is direct manipulation of the touch controller’s data stream, which would require physical proximity or compromised firmware controlling the controller. Once exploited, the driver will accept the malformed data and corrupt the touch state, potentially disrupting touch‑enabled user interfaces.