CVE-2024-56663 is a vulnerability identified in the Linux kernel's wireless networking subsystem, specifically within the nl80211 interface handling the NL80211_ATTR_MLO_LINK_ID attribute. The issue arises due to an off-by-one error in the validation of this netlink attribute's range. The Linux kernel uses inclusive range checks for netlink attributes, but the maximum allowed value for NL80211_ATTR_MLO_LINK_ID was incorrectly set to IEEE80211_MLD_MAX_NUM_LINKS instead of IEEE80211_MLD_MAX_NUM_LINKS - 1. This off-by-one mistake leads to an out-of-bounds access when the attribute value equals the maximum, causing a wild memory access. The vulnerability was demonstrated by a kernel address sanitizer (KASAN) crash in the ieee80211_tx_control_port function, which is part of the mac80211 wireless stack. The crash occurs due to a read of memory beyond the intended buffer, triggered by malformed netlink messages sent to the kernel's wireless subsystem. This flaw can lead to kernel crashes (denial of service) or potentially allow an attacker to execute arbitrary code in kernel space if exploited further. The vulnerability affects multiple Linux kernel versions as indicated by the affected commit hashes. The root cause is a logic error in the policy validation for netlink attributes, which has been corrected by adjusting the maximum allowed attribute value to prevent out-of-bounds access. No known exploits are currently reported in the wild, but the vulnerability resides in a critical kernel component responsible for wireless communication, making it a significant risk if weaponized.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable Linux kernel versions with wireless networking enabled. Given the widespread use of Linux in enterprise servers, cloud infrastructure, and embedded devices across Europe, exploitation could lead to kernel crashes causing denial of service or potentially privilege escalation if combined with other vulnerabilities. This could disrupt critical services, especially in sectors reliant on wireless connectivity such as telecommunications, manufacturing, and public infrastructure. Additionally, organizations using Linux-based wireless access points or IoT devices could see increased exposure. The potential for remote exploitation via crafted netlink messages means attackers could target exposed systems over the network, increasing the threat surface. The lack of known exploits currently limits immediate risk, but the vulnerability's presence in the kernel wireless stack makes it a high-value target for attackers aiming to compromise Linux hosts.

European organizations should promptly update their Linux kernel to the patched versions that correct the off-by-one validation error in the nl80211 subsystem. Kernel updates should be prioritized on systems with wireless networking enabled, especially those exposed to untrusted networks. Network segmentation can reduce exposure by isolating critical Linux hosts from untrusted wireless networks. Employing kernel hardening features such as Kernel Address Sanitizer (KASAN) in testing environments can help detect similar issues early. Monitoring kernel logs for unusual wireless subsystem errors or crashes can provide early warning signs of exploitation attempts. For embedded and IoT devices running Linux, vendors should be contacted to ensure firmware updates addressing this vulnerability are applied. Additionally, restricting netlink socket access to trusted users and processes can limit the ability of attackers to send malicious netlink messages. Organizations should also review their incident response plans to include scenarios involving kernel-level wireless subsystem compromises.