CVE-2023-54240: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54240 is a NULL pointer dereference vulnerability in the Linux kernel's MediaTek Ethernet driver (mtk_eth_soc), specifically in the mtk_hwlro_get_fdir_all() function. The flaw arises because rule_locs, allocated in ethtool_get_rxnfc with a size determined by user-supplied rule_cnt, is used without first validating rule_cnt, potentially resulting in a NULL pointer dereference. The vulnerability affects the Linux kernel across multiple stable branches prior to the patched versions. It was published on December 30, 2025, and carries an EPSS score of 0.024% (very low probability of exploitation) (Feedly, ENISA EUVD). No CVSS base score has been assigned by the authoritative sources at this time.

The root cause is a missing input validation check (CWE-476: NULL Pointer Dereference) in the mtk_hwlro_get_fdir_all() function within the MediaTek Ethernet SoC driver (net/ethernet/mtk_eth_soc.c). When a user-space application calls the ethtool interface with ETHTOOL_GRXCLSRLALL, the kernel allocates rule_locs based on the user-supplied rule_cnt value; if rule_cnt is zero or invalid, rule_locs may be NULL, and subsequent use of this pointer without validation causes a kernel NULL pointer dereference. The fix adds a check on rule_cnt before accessing rule_locs. Patches were applied across multiple stable kernel branches (Feedly, ENISA EUVD).

Successful exploitation of this vulnerability could cause a kernel panic or system crash (denial of service) on affected Linux systems using the MediaTek Ethernet SoC driver. Because the vulnerability is triggered via the ethtool interface, exploitation typically requires local access with sufficient privileges to invoke ethtool operations. There is no evidence of confidentiality or integrity impact; the primary risk is availability loss on embedded or networking devices using the affected MediaTek hardware (Feedly, ENISA EUVD).

Apply the upstream Linux kernel patches that add the rule_cnt validation check in mtk_hwlro_get_fdir_all(). Fixed versions include: Linux 4.14.326, 4.19.295, 5.4.257, 5.10.195, 5.15.132, 6.1.54, 6.5.4, and 6.6 (stable). Users running affected kernel versions on MediaTek Ethernet SoC hardware should update to the appropriate patched stable release. As a temporary workaround, restricting unprivileged user access to ethtool operations can reduce exposure (ENISA EUVD, Feedly).