CVE-2023-53088 is a use-after-free (UaF) vulnerability identified in the Linux kernel's Multipath TCP (MPTCP) implementation, specifically in the listener shutdown path. MPTCP is an extension of TCP that allows multiple paths to be used simultaneously between two endpoints, improving redundancy and throughput. The vulnerability arises due to a race condition where the grace period for the msk (multipath socket) can expire between the last reference count decrement in the function mptcp_subflow_queue_clean() and a subsequent access in inet_csk_listen_stop(). This leads to a use-after-free condition where the kernel attempts to access memory that has already been freed, causing instability and potential kernel crashes. The issue was introduced after a refactoring of the passive socket initialization and is triggered during the shutdown of MPTCP listener sockets. The kernel's Kernel Address Sanitizer (KASAN) detected this bug, indicating a write of size 4 to a freed memory address during the execution of the syz-executor731 task, a fuzzing tool used for kernel testing. The vulnerability can cause kernel panics or denial of service (DoS) conditions due to corrupted kernel memory. The fix involves removing unnecessary special-case code for msk listener socket cleanup and relying on the MPTCP worker to process unaccepted msk sockets properly, preventing premature freeing of memory. This patch depends on prior commits that refactor passive socket initialization and use workqueues to destroy unaccepted sockets safely. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable versions of the Linux kernel with MPTCP enabled or in use. Given Linux's widespread deployment in servers, cloud infrastructure, and embedded devices across Europe, exploitation could lead to kernel crashes and denial of service, disrupting critical services and applications. Organizations relying on MPTCP for network resilience or performance could experience instability or outages, impacting availability. While the vulnerability does not directly allow privilege escalation or remote code execution, the resulting kernel instability could be leveraged as part of a larger attack chain or cause significant operational disruption. Industries with high dependence on Linux-based infrastructure, such as telecommunications, finance, and cloud service providers, may face increased risk. Additionally, embedded systems and IoT devices running affected kernels could be impacted, potentially affecting industrial control systems or critical infrastructure. The lack of known exploits reduces immediate risk, but the vulnerability's presence in the kernel means that attackers with local access could trigger it, emphasizing the need for timely patching.

European organizations should prioritize updating Linux kernel versions to those including the fix for CVE-2023-53088. Specifically, kernel versions incorporating the patches that refactor passive socket initialization and use workqueues for socket destruction should be deployed. System administrators should audit their environments to identify systems running vulnerable kernel versions, especially those utilizing MPTCP features. If MPTCP is not required, disabling it at the kernel configuration or runtime level can reduce the attack surface. For environments where kernel updates are delayed, applying kernel live patching solutions, if available, can mitigate risk without downtime. Monitoring kernel logs for KASAN reports or unusual socket shutdown errors can help detect attempts to trigger the vulnerability. Network segmentation and strict access controls should be enforced to limit local access to trusted users, as exploitation requires local code execution. Finally, organizations should maintain robust backup and recovery procedures to minimize impact from potential kernel crashes or DoS conditions.