CVE-2023-52701 is a vulnerability identified in the Linux kernel affecting the handling of socket buffer (skb) marks during user-space copying operations. The issue arises specifically when the kernel is configured with CONFIG_HARDENED_USERCOPY enabled, a security feature designed to prevent kernel memory exposure by enforcing strict checks on memory copying between kernel and user space. The vulnerability was discovered through syzbot, an automated kernel fuzzer, which found that arm64 Linux kernel builds would crash in the function sock_recv_mark() due to improper handling of skb->mark data. The root cause is that only the skb->cb[] field is safe to copy directly to or from user space, as per kernel commit 79a8a642bf05, but the vulnerable code attempted to copy skb->mark without using a bounce buffer, leading to a kernel BUG triggered by a usercopy memory exposure detection. Architectures like x86 and powerpc do not currently detect this issue because they define user_access_begin, which handles the problem differently, but arm64 lacks this safeguard. The vulnerability can cause kernel crashes (denial of service) and potentially expose kernel memory contents to user space, which could lead to information disclosure or privilege escalation if exploited. The patch involves using a bounce buffer to safely copy skb->mark data, preventing direct copying that violates hardened usercopy constraints. The vulnerability affects Linux kernel versions prior to the patch and is particularly relevant for systems running arm64 architecture with hardened usercopy enabled. No known exploits are reported in the wild as of the publication date.

For European organizations, the impact of CVE-2023-52701 can be significant, especially for those relying on arm64-based Linux servers or embedded devices with hardened usercopy enabled. The vulnerability can cause kernel panics leading to denial of service, disrupting critical services and operations. Additionally, the potential for kernel memory exposure could allow attackers to leak sensitive information or escalate privileges, compromising confidentiality and integrity of systems. This is particularly concerning for sectors such as finance, healthcare, telecommunications, and government infrastructure, where Linux servers are widely deployed. The arm64 architecture is increasingly common in cloud environments and edge computing devices, which are prevalent in Europe’s digital infrastructure. Organizations using Linux kernels without the patch risk operational instability and security breaches. Although no active exploits are known, the vulnerability’s presence in the kernel codebase means attackers with local access could attempt to trigger the flaw, emphasizing the need for timely mitigation.

European organizations should prioritize updating their Linux kernels to the latest patched versions that include the fix for CVE-2023-52701. Specifically, ensure that all arm64 systems with CONFIG_HARDENED_USERCOPY enabled are upgraded. For environments where immediate patching is challenging, consider disabling CONFIG_HARDENED_USERCOPY temporarily only if the risk of kernel memory exposure is outweighed by operational needs, but this is not recommended as a long-term solution. Implement strict access controls to limit local user access to trusted personnel and processes, reducing the risk of exploitation. Employ kernel crash monitoring and alerting to detect and respond to any kernel panics that may indicate attempted exploitation. Additionally, review and harden user-space applications interacting with socket buffers to minimize exposure. For cloud and containerized environments, ensure base images are updated and redeployed promptly. Regularly audit kernel configurations and maintain an inventory of affected systems to ensure comprehensive coverage of mitigation efforts.