CVE-2024-37356 is a vulnerability identified in the Linux kernel's implementation of the DCTCP (Data Center TCP) congestion control algorithm, specifically within the function dctcp_update_alpha(). The issue arises from an unchecked module parameter, dctcp_shift_g, which controls bit-shift operations on 32-bit unsigned integers. The vulnerability was discovered through fuzz testing by syzkaller, which demonstrated that setting dctcp_shift_g to an excessively high value (e.g., 100) causes a shift-out-of-bounds error. This occurs because the code performs bit-shift operations without validating that the shift amount is within the valid range for a 32-bit integer, leading to undefined behavior and potential kernel instability or crashes. The patch introduced limits the maximum value of dctcp_shift_g to 10 using param_set_uint_minmax(), preventing out-of-bounds shifts. The vulnerability is rooted in improper input validation of kernel module parameters, which can be manipulated by users with write access to /sys/module/tcp_dctcp/parameters/dctcp_shift_g. Exploitation requires the ability to write to this sysfs parameter, typically restricted to privileged users or processes. The vulnerability does not appear to be exploited in the wild yet, and no CVSS score has been assigned. The underlying issue is a classic integer shift error that can cause kernel panics or denial of service due to unstable kernel state. The vulnerability affects Linux kernel versions containing the vulnerable dctcp_update_alpha() implementation prior to the patch limiting dctcp_shift_g values.

For European organizations, the primary impact of CVE-2024-37356 is the risk of denial of service (DoS) on Linux systems running affected kernel versions with the DCTCP module enabled. Since DCTCP is often used in data center environments to optimize TCP congestion control, servers and network infrastructure relying on this feature could experience kernel crashes or instability if an attacker or misconfigured process sets dctcp_shift_g to an invalid value. This could disrupt critical services, especially in cloud hosting providers, telecom operators, and enterprises with Linux-based network appliances. Confidentiality and integrity impacts are minimal as the vulnerability does not directly allow code execution or privilege escalation but could be leveraged as part of a broader attack chain to cause service outages. The requirement for write access to kernel module parameters limits the attack surface to privileged insiders or compromised processes. However, in multi-tenant environments common in Europe’s cloud and hosting sectors, a malicious tenant with elevated privileges might exploit this to disrupt co-hosted services. The vulnerability also poses operational risks during kernel upgrades or parameter tuning if not properly controlled. Overall, the impact is primarily availability-related, affecting service continuity and potentially causing operational downtime.

European organizations should apply the official Linux kernel patch that restricts the dctcp_shift_g parameter to a maximum value of 10, preventing out-of-bounds shifts. System administrators must audit and restrict write permissions to /sys/module/tcp_dctcp/parameters/dctcp_shift_g to trusted users only, ensuring unprivileged users cannot modify this parameter. Monitoring tools should be configured to alert on unusual writes or attempts to change kernel module parameters related to TCP congestion control. For environments using custom kernel builds or older distributions, backporting the patch or upgrading to a kernel version containing the fix is critical. Network operators should review their use of DCTCP and consider disabling or restricting this module if not required. Additionally, implementing strict access controls and privilege separation on Linux hosts will reduce the risk of exploitation. Regular kernel updates and vulnerability scanning should be part of the security hygiene to detect and remediate such issues promptly. Finally, testing kernel parameter changes in staging environments before production deployment can prevent accidental misconfigurations that might trigger this vulnerability.