CVE-2025-37915 is a vulnerability identified in the Linux kernel's network scheduling subsystem, specifically within the Deficit Round Robin (drr) queuing discipline (qdisc) when used in conjunction with a netem child qdisc. The issue arises due to a reentrancy problem in the enqueue callback of the parent qdisc caused by certain use cases involving netem as a child. While this does not lead to a use-after-free (UAF) condition, the vulnerability causes the same classifier to be added twice to the active_list, resulting in memory corruption. This memory corruption can lead to unpredictable kernel behavior, including potential crashes or data integrity issues. The patch addressing this vulnerability adds a check to ensure that a class is not added twice to the active_list by verifying if it is already active (cl_is_active) before insertion, in addition to the existing check for queue length being zero. The vulnerability was reported by Gerrard and publicly disclosed on May 20, 2025. It affects Linux kernel versions identified by the commit hash 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and potentially other versions sharing the same code base. 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 Linux kernel versions with network scheduling configurations that use the drr qdisc with netem as a child. The impact includes potential kernel memory corruption leading to system instability or crashes, which could disrupt critical network services or infrastructure. In environments where Linux servers handle network traffic shaping or emulation—such as ISPs, telecom providers, cloud service providers, and enterprises with complex network setups—this could degrade service availability. Although no direct remote code execution or privilege escalation is indicated, memory corruption vulnerabilities in the kernel can sometimes be leveraged for more severe attacks if combined with other vulnerabilities. Therefore, the vulnerability could be a stepping stone for attackers aiming to disrupt operations or cause denial of service. Given the widespread use of Linux in European data centers, cloud environments, and embedded systems, the potential impact is significant, especially for organizations relying on precise network traffic control and quality of service.

European organizations should prioritize updating their Linux kernels to versions that include the patch for CVE-2025-37915 as soon as it becomes available. Since the vulnerability is related to specific network scheduling configurations, administrators should audit their systems to identify usage of the drr qdisc with netem as a child. Where feasible, temporarily disabling or reconfiguring these qdiscs to avoid the vulnerable code path can reduce risk until patches are applied. Network administrators should also monitor kernel logs and system stability for signs of memory corruption or crashes that could indicate exploitation attempts. Implementing strict access controls and limiting administrative privileges can reduce the risk of exploitation. Additionally, organizations should maintain robust backup and recovery procedures to mitigate the impact of potential system crashes. For environments where patching is delayed, deploying network segmentation and isolating critical systems can limit exposure. Finally, staying informed through Linux kernel mailing lists and security advisories will help organizations respond promptly to any emerging exploit reports.