CVE-2025-37752 is a vulnerability identified in the Linux kernel's network scheduler component, specifically within the 'sch_sfq' (Stochastic Fairness Queueing) queuing discipline implementation. The issue arises from insufficient validation of the 'limit' parameter during configuration updates. Initially, the limit was validated only on direct user input; however, it could be indirectly modified through changes to other parameters such as 'flows' and 'divisor'. This flaw allowed scenarios where the limit value could become inconsistent or out-of-bounds, leading to an array index out-of-bounds error in the 'sfq_head' array. The vulnerability was discovered through syzkaller fuzz testing, which triggered a crash due to an out-of-bounds access at net/sched/sch_sfq.c line 203. The root cause is that the validation check was performed too early in the configuration update process, missing indirect updates to the limit. The fix involved moving the limit validation to the end of the configuration update process to ensure all parameter interactions are accounted for before applying the limit. This prevents invalid configurations that could cause kernel crashes or undefined behavior. The vulnerability affects multiple Linux kernel versions as indicated by the affected commit hashes. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations relying on Linux-based systems, especially those using advanced network traffic control features like SFQ for managing network queues, this vulnerability poses a risk of local denial of service (DoS) through kernel crashes. Attackers with the ability to configure network queuing disciplines (typically requiring root or elevated privileges) could exploit this flaw to cause system instability or crashes, potentially disrupting network services or impacting availability. While remote exploitation is unlikely without prior access, compromised insiders or attackers with administrative access could leverage this bug to escalate disruption. Critical infrastructure providers, cloud service operators, and enterprises with Linux-based networking equipment or servers could see service interruptions. Additionally, embedded Linux devices used in industrial control systems or telecommunications within Europe might be affected if they use vulnerable kernel versions. The vulnerability does not appear to allow privilege escalation or remote code execution directly but could be used as part of a multi-stage attack to degrade system reliability or availability.

1. Apply the official Linux kernel patches that move the limit validation to the end of the configuration update process as soon as they become available. Monitor Linux kernel mailing lists and vendor advisories for updates. 2. Restrict access to network configuration utilities such as 'tc' (traffic control) to trusted administrators only, minimizing the risk of unauthorized exploitation. 3. Implement strict access controls and auditing on systems that allow network queue configuration changes to detect and prevent suspicious activities. 4. For environments using automated configuration management, validate configurations to avoid setting parameters that could indirectly cause invalid limit values. 5. In critical environments, consider temporarily disabling or avoiding the use of the SFQ queuing discipline until patched, or switch to alternative queuing disciplines not affected by this vulnerability. 6. Conduct thorough testing of network configurations after patching to ensure stability and correct behavior. 7. Maintain up-to-date backups and incident response plans to quickly recover from potential DoS incidents caused by exploitation attempts.