CVE-2023-54193: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54193 is a use-after-free vulnerability in the Linux kernel's network traffic control subsystem (net/sched: cls_api). The flaw occurs in the error handling path of tcf_block_bind(), which frees flow_block_cb instances that have already been added to the driver list, leaving dangling pointers. It was published on December 30, 2025, and affects the Linux kernel (vendor: linux, product: kernel). No CVSS score has been officially assigned at this time (Feedly).

The root cause is a use-after-free (CWE-416) in net/sched/cls_api.c. When tcf_block_bind() encounters an error, its cleanup path frees all flow_block_cb instances in bo->cb_list. However, these instances were already inserted into the driver's list by the ndo_setup_tc() callback (called earlier in tcf_block_offload_cmd()), so the driver list retains dangling pointers to freed memory. A subsequent call to flow_block_cb_setup_simple() then dereferences these freed objects, triggering a KASAN-detected slab-use-after-free at ffff888147e2bf20. The fix removes flow_block_cb instances from the driver list before deallocating them in the error path (Feedly).

Successful exploitation of this vulnerability could allow a local attacker with sufficient privileges to manipulate kernel memory, potentially leading to kernel crashes (denial of service) or, in more sophisticated scenarios, privilege escalation or arbitrary code execution in kernel context. The affected component is the Linux kernel's traffic control classifier API, which is accessible to users with CAP_NET_ADMIN capability. The scope is limited to the local system, but kernel-level compromise could enable full system takeover (Feedly).

The fix has been committed to the Linux kernel stable tree across multiple stable branches, with patches available at the official kernel.org git repository (commits 7b7a74ed303d, 26aec72429a0, 7311c8be3755, 55866fe3fded, and cb145932fcf6). System administrators should update to a patched kernel version that includes these commits. As a workaround, restricting access to CAP_NET_ADMIN capabilities (e.g., via user namespaces or seccomp policies) can reduce exposure until a patched kernel is deployed (Feedly).