CVE-2023-54186: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54186 is a use-after-free vulnerability in the Linux kernel's USB Type-C DisplayPort alternate mode driver (usb/typec/altmodes/displayport). The flaw exists in the pin_assignment_show function, which performs negative indexing of the buf array when get_current_pin_assignments returns 0 (i.e., no compatible pin assignments are found), triggering a KASAN-detected use-after-free condition. It affects Linux kernel versions from commit 0e3bb7d6894d9b6e67d6382bb03a46a1dc989588 up to the respective fix commits across multiple stable branches. Patches were backported to stable releases including 4.19.284, 5.4.244, 5.10.181, 5.15.113, 6.1.30, 6.3.4, and 6.4. The vulnerability was published on December 30, 2025, and carries a medium severity estimate with an EPSS score of approximately 0.032% (Feedly, ENISA EUVD).

The root cause is an off-by-one/negative index bug (CWE-125: Out-of-bounds Read, related to CWE-416: Use After Free) in the pin_assignment_show sysfs attribute handler within drivers/usb/typec/altmodes/displayport.c. When get_current_pin_assignments() returns 0, the subsequent decrement operation produces a negative index into the buf character array, causing the function to read memory before the buffer's start — a condition detected by KASAN as a use-after-free. The KASAN call trace confirms the fault occurs at pin_assignment_show+0x26c/0x33c on ARM64 systems, triggered via the dev_attr_show sysfs interface. Exploitation would require local access to a system with a USB Type-C DisplayPort alternate mode device attached and the ability to read the relevant sysfs attribute (Feedly, ENISA EUVD).

The primary impact is a kernel memory safety violation that can cause system instability or a kernel panic (denial of service) when the vulnerable sysfs attribute is read under the triggering condition. On systems with KASAN enabled, the bug is reliably detected and reported; on production kernels without KASAN, the out-of-bounds read may silently corrupt memory or cause unpredictable behavior. The confidentiality impact is limited, as the out-of-bounds read exposes a small region of kernel memory adjacent to the buffer, but the integrity and availability risks (kernel crash, memory corruption) are the primary concerns (Feedly).

Apply the upstream kernel patches that fix the negative indexing in pin_assignment_show. Fixed versions are available in the following stable releases: 4.19.284, 5.4.244, 5.10.181, 5.15.113, 6.1.30, 6.3.4, and 6.4. Administrators running affected kernel versions should update to a patched release via their distribution's package manager or by applying the relevant stable kernel commits. As a temporary workaround on systems where USB Type-C DisplayPort alternate mode is not required, disabling or blacklisting the typec_displayport kernel module can prevent the vulnerable code path from being reached (ENISA EUVD, Feedly).