The Linux kernel vulnerability CVE-2026-64085 affects the hwmon subsystem's pmbus/adm1266 driver. The adm1266_pmbus_block_xfer() helper function copies device-supplied block payloads into a caller-provided buffer trusting the device-supplied length without boundary checks. The caller function adm1266_nvmem_read_blackbox() reads blackbox records in 64-byte increments but the helper can write up to 255 bytes, causing a buffer overflow of up to 191 bytes in the 2048-byte device memory allocation. The vulnerability is addressed by introducing a local bounce buffer of 255 bytes to safely receive the data, validating the length returned, and copying only the fixed 64-byte record size into the device memory buffer, thus preventing overflow without changing the helper function's signature.

This vulnerability can cause a buffer overflow in kernel memory when processing device-supplied data, potentially leading to memory corruption. The overflow occurs in the device memory buffer used by the adm1266 driver. Although no known exploits are reported in the wild, such memory corruption could lead to system instability or escalation of privileges if exploited.

A fix has been implemented in the Linux kernel source code that safely handles the device-supplied data by using a local bounce buffer and validating the length before copying to the device memory buffer. Users should update their Linux kernel to a version that includes this fix once available. Patch status is not yet confirmed in the provided data; check the official Linux kernel advisories or vendor updates for the specific patched versions and apply the update accordingly.