CVE-2023-54299: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54299 is a NULL pointer dereference vulnerability in the Linux kernel's USB Type-C Alt Mode bus driver (typec_altmode_attention). It affects Linux kernel versions from commit 8a37d87d72f0 up to multiple stable branch fix points, spanning kernel versions 4.19 through pre-6.6. The vulnerability was published on December 30, 2025, and has a CVSS v3.1 base score of 5.5 (Medium) (Red Hat CVE, Feedly).

The root cause is a missing NULL pointer check (CWE-476) in the typec_altmode_attention() function within the Linux kernel's USB Type-C bus driver (drivers/usb/typec/bus.c). When a USB hub negotiates DisplayPort Alt mode with a connected device and subsequently performs a data role swap, the device unregisters all Alt modes. However, the hub continues to send Attention messages; typec_altmode_attention does not verify whether the Alt Mode partner still exists before dereferencing typec_altmode and typec_altmode_ops structures, resulting in a NULL pointer dereference. The fix adds a partner existence check before forwarding the Attention message to the Alt Mode driver (Red Hat CVE, EUVD).

Successful exploitation causes a kernel crash, resulting in a denial of service (system unavailability). The impact is limited to availability — there is no confidentiality or integrity impact. An attacker with local access and low privileges who can connect a malicious or specially crafted USB hub device can trigger the crash, potentially affecting any system using USB Type-C docking stations, hubs, or DisplayPort Alt mode-capable devices (Feedly, Red Hat CVE).

Patches have been merged into multiple Linux kernel stable branches. Fixed versions include: 5.4.257, 5.10.195, 5.15.132, 6.1.53, 6.4.16, 6.5.3, and 6.6. Organizations should update to a patched kernel version as the primary remediation. As a temporary workaround, restricting physical USB port access on sensitive systems can reduce exposure until patches are applied, since exploitation requires connecting a malicious USB device (Red Hat CVE, EUVD).