CVE-2024-38633 is a vulnerability identified in the Linux kernel's MAX3100 serial driver, specifically related to the UART (Universal Asynchronous Receiver/Transmitter) driver registration and removal process. The issue arises when the last MAX3100 device is removed, triggering the removal of the driver. However, the kernel code fails to update a global variable that tracks whether the UART driver is registered. This leads to a kernel NULL pointer dereference (kernel oops) after a cycle of inserting and removing the module (insmod — rmmod — insmod). The error manifests as a crash in the serial_core_register_port function, indicating improper handling of driver state during probe and removal operations. The root cause is that the global variable controlling the driver's registration state is not cleared or updated correctly after driver removal, causing subsequent driver registration attempts to operate on invalid state and resulting in kernel crashes. The fix involves updating the global state variable only after a successful uart_register_driver() call, ensuring the driver state is consistent and preventing kernel oopses during module reload cycles. This vulnerability affects Linux kernel versions identified by the commit hash 7831d56b0a3544cbb6f82f76c34ca95e24d5b676 and likely other versions containing the same faulty logic in the MAX3100 UART driver. Although no known exploits are reported in the wild, the vulnerability can cause denial of service due to kernel crashes when the affected driver is loaded and unloaded repeatedly.

For European organizations, the impact of CVE-2024-38633 primarily involves system stability and availability risks on Linux systems utilizing the MAX3100 serial driver. This driver is typically used in embedded systems or specialized hardware interfacing with UART serial ports. A kernel oops leading to a crash can cause service interruptions, potentially affecting critical infrastructure, industrial control systems, or network devices relying on Linux kernels with this driver. While the vulnerability does not directly lead to privilege escalation or data breaches, the denial of service caused by kernel crashes can disrupt operations, especially in environments where uptime and reliability are critical, such as manufacturing, telecommunications, and transportation sectors. Systems that frequently load and unload the MAX3100 driver, or that dynamically manage serial devices, are at higher risk. The absence of known exploits reduces immediate threat levels, but unpatched systems remain vulnerable to accidental or malicious triggering of kernel crashes, which could be leveraged in targeted denial-of-service attacks.

European organizations should apply the official Linux kernel patches that address CVE-2024-38633 as soon as they become available. Until patches are deployed, organizations should minimize the loading and unloading cycles of the MAX3100 driver to reduce the risk of kernel crashes. System administrators should audit their Linux systems to identify the presence and usage of the MAX3100 driver, especially in embedded or industrial environments. For critical systems, consider isolating or restricting access to devices using this driver to prevent unauthorized module reloads. Monitoring kernel logs for oops or crash messages related to serial_core_register_port or max3100_probe can help detect attempts to trigger this vulnerability. Additionally, organizations should implement robust backup and recovery procedures to quickly restore systems in case of crashes. For environments where patching is delayed, consider using kernel lockdown or module signing features to prevent unauthorized module insertion/removal that could trigger the vulnerability.