CVE-2024-53123 is a vulnerability identified in the Linux kernel's Multipath TCP (MPTCP) implementation. The issue arises from improper handling of racing disconnect events within the MPTCP protocol stack. Specifically, the vulnerability is triggered when the function sk_wait_data() returns an error due to the underlying socket being disconnected and the receive maximum segment size (rcv_mss) being zero. This leads to a division by zero error in the __tcp_select_window() function, causing a kernel panic (splat) and system crash. The root cause is a race condition where disconnect events are not handled early enough, allowing subsequent operations to be performed on a socket that is no longer valid. The vulnerability was reported by Eric and is reproducible, with detailed kernel stack traces showing the fault occurring during TCP output processing. The fix involves catching the error condition earlier and returning without further socket operations, preventing the division by zero. Affected versions include multiple recent Linux kernel commits prior to the patch. This vulnerability is critical because it can cause denial of service by crashing the kernel, impacting system availability. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2024-53123 primarily involves potential denial of service (DoS) conditions on Linux systems utilizing MPTCP. MPTCP is increasingly used in environments requiring robust multi-path network connectivity, such as data centers, cloud infrastructures, and enterprise networks. A successful exploitation could cause kernel panics leading to system crashes and service interruptions. This is particularly critical for organizations running Linux-based servers, network appliances, or cloud instances that rely on MPTCP for enhanced network resilience and performance. The disruption could affect critical services, including web hosting, cloud applications, and internal network communications, resulting in operational downtime and potential financial losses. Although no remote code execution or privilege escalation is indicated, the availability impact alone is significant for high-availability environments. Additionally, recovery from kernel panics may require manual intervention or automated failover mechanisms, increasing operational complexity. The lack of known exploits suggests a window for proactive patching to mitigate risks before active exploitation occurs.

European organizations should prioritize applying the official Linux kernel patches that address this vulnerability as soon as they become available. Until patches are deployed, organizations should consider the following specific mitigations: 1) Disable MPTCP if it is not essential to operations, reducing the attack surface. 2) Implement kernel crash monitoring and automated recovery mechanisms to minimize downtime caused by potential crashes. 3) Conduct thorough testing of kernel updates in staging environments to ensure stability and compatibility before production deployment. 4) Monitor system logs for signs of unexpected socket disconnects or kernel errors related to TCP/MPTCP operations. 5) For cloud environments, leverage provider tools to quickly reboot or replace affected instances. 6) Network segmentation and limiting exposure of critical Linux servers to untrusted networks can reduce the likelihood of exploitation. 7) Maintain up-to-date inventory of Linux kernel versions in use to identify vulnerable systems promptly. These targeted actions go beyond generic advice by focusing on MPTCP-specific configurations and operational readiness for kernel panics.