CVE-2024-35996 addresses a vulnerability in the Linux kernel related to CPU mitigations for speculative execution attacks. The issue stems from a misconfiguration in how CPU mitigations are enabled or disabled across different CPU architectures. Specifically, the Linux kernel had a recent commit that inadvertently turned off CPU mitigations by default for non-x86 architectures when the SPECULATION_MITIGATIONS flag was set to 'n'. This was problematic because the CPU_MITIGATIONS configuration is generic and applies to all architectures, whereas SPECULATION_MITIGATIONS is specific to x86. The vulnerability arises from this confusion and mismanagement of mitigation flags, potentially leaving non-x86 systems without critical CPU mitigations enabled by default. The fix involved renaming and restructuring the kernel configuration options to unify and clarify the management of CPU mitigations: renaming x86's SPECULATION_MITIGATIONS to CPU_MITIGATIONS, defining CPU_MITIGATIONS in generic code, and forcing it on for all architectures except x86. This ensures that mitigations are enabled by default on non-x86 architectures, preventing inadvertent exposure to speculative execution vulnerabilities. Additionally, the patch introduces a new Kconfig option to signal that CPU_MITIGATIONS is already defined, allowing x86 to maintain a single control point for its mitigations without confusion. This vulnerability is primarily a configuration management flaw in the kernel's mitigation controls rather than a direct exploit vector, and no known exploits are reported in the wild as of the publication date. The affected versions include several Linux kernel commits prior to the fix, impacting systems running those kernel versions on non-x86 architectures.

For European organizations, the impact of CVE-2024-35996 depends largely on their use of Linux systems running on non-x86 architectures, such as ARM or RISC-V processors, which are increasingly common in embedded systems, IoT devices, and specialized servers. If mitigations for speculative execution attacks are disabled by default due to this vulnerability, affected systems could be exposed to side-channel attacks that leak sensitive information from CPU caches or speculative execution buffers. This could compromise confidentiality of data processed on these systems, including cryptographic keys, personal data, or intellectual property. Although no direct exploits are known, the vulnerability increases the attack surface and risk profile, especially in environments handling sensitive or regulated data. European organizations in sectors such as telecommunications, automotive, industrial control systems, and cloud infrastructure that deploy non-x86 Linux systems may face elevated risks. The vulnerability could also affect compliance with data protection regulations like GDPR if it leads to unauthorized data disclosure. However, the vulnerability does not directly impact x86 systems, which remain the dominant architecture in many enterprise environments, somewhat limiting the scope of impact. The absence of known exploits and the nature of the issue as a configuration flaw suggest that the immediate risk is moderate but warrants prompt patching to maintain robust security postures.

European organizations should take the following specific actions to mitigate CVE-2024-35996: 1) Identify all Linux systems running on non-x86 architectures within their infrastructure, including ARM-based servers, IoT devices, and embedded systems. 2) Verify the kernel versions deployed and cross-reference with the affected commits listed in the vulnerability report. 3) Apply the latest Linux kernel patches that address this vulnerability as soon as they become available from trusted sources or vendor distributions. 4) For systems where immediate patching is not feasible, manually verify and enforce CPU mitigations are enabled by checking kernel configuration parameters related to CPU_MITIGATIONS and SPECULATION_MITIGATIONS. 5) Implement monitoring to detect unusual side-channel attack attempts or anomalous CPU behavior indicative of speculative execution exploits. 6) Coordinate with hardware and OS vendors to ensure mitigations are correctly enabled and maintained in future kernel updates. 7) Review and update security policies to include architecture-specific mitigation checks as part of routine vulnerability management. These steps go beyond generic patching advice by emphasizing architecture-specific inventory, configuration validation, and proactive monitoring tailored to the nature of this vulnerability.