CVE-2023-54091: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54091 is a memory leak vulnerability in the Linux kernel's DRM (Direct Rendering Manager) subsystem, specifically within the drm_client_target_cloned function. The flaw occurs because dmt_mode is allocated via drm_mode_duplicate but never freed, affecting most drivers using the generic fbdev setup — most notably the AST (ASPEED) driver. The vulnerability was disclosed on December 24, 2025, and affects Linux kernel versions from 2.6.35 up through those prior to the patched stable releases. It carries a CVSS v3.1 base score of 5.5 (Medium) (Red Hat CVE, Feedly).

The root cause is a missing memory deallocation (CWE-401: Missing Release of Memory after Effective Lifetime) in the drm_client_target_cloned function within the kernel's DRM client layer. When the function allocates a dmt_mode object via drm_mode_duplicate and subsequently exits without freeing it — for example, when a cloned mode is not ultimately selected — the allocated 128-byte object is leaked. The kmemleak tool identified the leak through the call chain: drm_mode_duplicate → drm_client_target_cloned → drm_client_modeset_probe → __drm_fb_helper_initial_config_and_unlock → drm_fbdev_client_hotplug → drm_client_register → ast_pci_probe. Exploitation requires local access and low privileges, as the leak is triggered during device probing and framebuffer initialization (Red Hat CVE, Red Hat Bugzilla).

The primary impact is a gradual availability degradation: repeated invocations of the affected code path (e.g., during hotplug events or system initialization) accumulate unreleased kernel memory, potentially leading to memory exhaustion, system performance degradation, and eventual instability or crash. There is no confidentiality or integrity impact, as the vulnerability does not expose sensitive data or allow unauthorized writes. The scope is limited to the local system, and lateral movement is not a concern (Feedly).

Patches have been released for multiple stable Linux kernel branches. The fixed versions are: 4.14.322, 4.19.291, 5.4.251, 5.10.188, 5.15.123, 6.1.42, 6.4.7, and 6.5. Administrators should update to the patched kernel version corresponding to their deployment branch. As a secondary measure, monitoring system memory usage for unexpected growth — particularly on systems with AST or other fbdev-based GPU drivers — can help detect the leak's effects before they cause instability (Red Hat Bugzilla, Feedly).