Medium [CVE-2026-63932] reject oversized serial replies

In the Linux kernel, the following vulnerability has been resolved: iio: chemical: mhz19b: reject oversized serial replies mhz19b_receive_buf() appends each serdev chunk into the fixed MHZ19B_CMD_SIZE receive buffer and advances buf_idx by len without checking that the chunk fits in the remaining space.

A large callback can therefore overflow st->buf before the command path validates the reply. Reset the reply state before each command and reject oversized serial replies before copying them into the fixed buffer.

When an oversized reply is detected, wake the waiter and report -EMSGSIZE instead of overwriting st->buf. A flaw was found in the Linux kernel's `mhz19b` driver, which handles Winsen MHZ19B CO2 sensors.

The `mhz19b_receive_buf()` function does not properly validate the size of incoming serial replies before copying them into a fixed-size buffer. A remote attacker could exploit this by sending an oversized serial reply, leading to a buffer overflow.

This could result in a denial of service or potentially more severe impacts by overwriting critical data within the kernel. Red Hat severity: Moderate.

Weakness: CWE-120. Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9 as not affected.