CVE-2024-36918 is a vulnerability identified in the Linux kernel's implementation of the Berkeley Packet Filter (BPF) subsystem, specifically related to the bloom filter map type. The issue arises from a missing validation check on the size of values used when creating bloom filter maps. The patch introduced adds a critical check to reject values exceeding KMALLOC_MAX_SIZE, which is the maximum size allowed for kernel memory allocations. Without this check, it is possible for value sizes to overflow integer variables, leading to kernel crashes. This vulnerability was discovered through fuzzing with syzkaller, a kernel fuzzing tool, which detected crashes caused by oversized bloom filter values. The problem stems from the bloom filter map not enforcing the same size constraints as other map types, resulting in potential integer overflow and subsequent kernel instability or denial of service. The Linux kernel maintainers have addressed this by adding the missing size check and further reinforcing guardrails at lower levels of the kernel memory allocation process. No known exploits are currently reported in the wild, and the vulnerability was published on May 30, 2024. The affected versions are identified by specific commit hashes, indicating that this is a recent and specific code regression or omission in the kernel source. The vulnerability impacts the kernel's stability and availability but does not directly indicate privilege escalation or data confidentiality compromise. However, kernel crashes can lead to denial of service conditions on affected systems.

For European organizations, this vulnerability primarily poses a risk to system availability and stability. Linux is widely used across Europe in servers, cloud infrastructure, embedded devices, and critical infrastructure systems. A kernel crash caused by exploitation or accidental triggering of this vulnerability could disrupt services, cause downtime, and impact business continuity. Organizations relying on Linux-based systems for critical operations, including telecommunications, finance, healthcare, and government services, could experience service interruptions. While there is no evidence of privilege escalation or data breach potential, denial of service attacks targeting this vulnerability could be leveraged by threat actors to degrade system reliability or as part of multi-stage attacks. The lack of known exploits reduces immediate risk, but the vulnerability’s presence in kernel code means that any unpatched system remains susceptible to accidental or malicious triggering. European cloud providers and data centers running Linux kernels with the vulnerable bloom filter implementation are particularly at risk, as kernel crashes could affect multiple tenants and services. Additionally, embedded Linux devices in industrial control systems or IoT deployments across Europe could be impacted, potentially affecting operational technology environments.

To mitigate this vulnerability, European organizations should prioritize updating their Linux kernel to the latest patched versions that include the fix for CVE-2024-36918. Kernel updates should be applied promptly, especially on production servers and critical infrastructure systems. Organizations should audit their systems to identify Linux kernel versions and verify if they include the patch rejecting bloom filter values exceeding KMALLOC_MAX_SIZE. For environments where immediate kernel upgrades are not feasible, implementing kernel crash monitoring and automated recovery mechanisms can reduce downtime impact. Additionally, restricting untrusted user access to BPF map creation or limiting capabilities that allow manipulation of bloom filter maps can reduce the attack surface. Security teams should monitor kernel logs for unusual BPF-related errors or crashes that could indicate attempted exploitation. Incorporating fuzz testing or kernel integrity monitoring in development and staging environments can help detect regressions or similar vulnerabilities early. Finally, organizations should maintain robust incident response plans to quickly address any kernel-level crashes or denial of service events.