CVE-2025-23138 is a vulnerability identified in the Linux kernel related to improper accounting of pipe buffer usage within the watch_queue subsystem. Specifically, the function watch_queue_set_size() modifies the pipe buffers charged to a user (user->pipe_bufs) without correspondingly updating the pipe's own accounting variable (pipe->nr_accounted). This discrepancy arises because pipe_resize_ring() contains a conditional check (!pipe_has_watch_queue()) that prevents updating pipe->nr_accounted when watch queues are involved. As a result, when the pipe is eventually freed, the decrement operation on user->pipe_bufs does not match the original increment, potentially causing an underflow. This underflow can lead to failures in subsequent checks such as too_many_pipe_buffers_soft(), which may return an -EPERM error code, indicating a permission error. The root cause appears to be a mismatch in accounting logic, possibly due to intentional overprovisioning in watch_queue_set_size(), though the exact rationale is unclear. The vulnerability affects multiple Linux kernel versions identified by specific commit hashes. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The issue is technical and subtle, involving kernel-level resource accounting that could impact system stability and resource management.

For European organizations relying heavily on Linux-based infrastructure, this vulnerability could lead to unexpected permission errors and resource accounting inconsistencies in kernel pipe buffers. This may manifest as application failures or degraded performance in systems that use pipes extensively for inter-process communication, such as web servers, database systems, and containerized environments. While the vulnerability does not directly allow privilege escalation or remote code execution, the underflow and accounting mismatch could be leveraged in complex attack chains or cause denial of service conditions by exhausting pipe buffer resources or causing kernel-level errors. Critical infrastructure, cloud service providers, and enterprises with large-scale Linux deployments could experience operational disruptions. Additionally, debugging and troubleshooting such subtle kernel issues can be time-consuming and costly. Given the Linux kernel's widespread use in European data centers, telecommunications, and government systems, the impact could be significant if unpatched.

Organizations should promptly apply the official Linux kernel patches that address this vulnerability once available. Since the issue involves kernel-level resource accounting, updating to a fixed kernel version is the most effective mitigation. In the interim, monitoring system logs for -EPERM errors related to pipe buffers and unusual pipe resource usage patterns can help detect potential exploitation or impact. Administrators should audit applications that heavily utilize pipes for inter-process communication and consider implementing resource limits or fallback mechanisms to handle pipe buffer errors gracefully. For environments using container orchestration platforms like Kubernetes, ensuring that the underlying node kernels are patched is critical. Additionally, engaging with Linux distribution vendors for backported fixes and security advisories will help maintain timely protection. Avoiding custom kernel modifications that alter pipe or watch_queue behavior is recommended to prevent exacerbating the issue.