CVE-2025-21770 is a vulnerability identified in the Linux kernel's IOMMU (Input-Output Memory Management Unit) subsystem, specifically within the function iopf_queue_remove_device(). This function is responsible for removing a device from the per-IOMMU IOPF (I/O Page Fault) queue when the Page Request Interface (PRI) is disabled on that device. The function handles outstanding IOPFs by responding with an IOMMU_PAGE_RESP_INVALID code and detaching the device from the queue. However, the vulnerability arises because after responding to the hardware, the function fails to release the group structure representing a collection of IOPFs awaiting response. This omission leads to a memory leak when iopf_queue_remove_device() is invoked with pending IOPFs. The memory leak occurs because the group structure is not freed, causing the kernel to retain allocated memory unnecessarily. The fix involves calling iopf_free_group() after the IOPF group has been responded to, ensuring proper cleanup of allocated resources. This vulnerability affects Linux kernel versions identified by the provided hashes, indicating specific commits or builds. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The vulnerability is technical and subtle, rooted in kernel memory management related to device IOMMU queues, and could potentially degrade system stability or lead to resource exhaustion over time if exploited or triggered repeatedly.

For European organizations, the impact of CVE-2025-21770 primarily concerns system stability and availability. The memory leak in the Linux kernel's IOMMU subsystem can cause gradual memory exhaustion on affected systems, potentially leading to degraded performance, system slowdowns, or crashes. This is particularly critical for environments running Linux servers with heavy I/O workloads or virtualization platforms that rely on IOMMU for device isolation and security. Data confidentiality and integrity are less directly impacted since the vulnerability does not enable privilege escalation or code execution. However, availability issues can disrupt critical services, especially in sectors such as finance, healthcare, telecommunications, and public infrastructure where Linux servers are prevalent. Over time, unmitigated memory leaks can increase operational costs due to increased maintenance, unexpected downtime, and potential cascading failures in complex systems. The lack of known exploits reduces immediate risk, but the vulnerability should be addressed proactively to maintain system reliability and security posture.

To mitigate CVE-2025-21770, European organizations should: 1) Apply the official Linux kernel patches that include the fix calling iopf_free_group() after responding to IOPF groups. Monitoring the Linux kernel mailing lists and vendor advisories for updated kernel versions is essential. 2) For environments where immediate patching is challenging, implement monitoring of kernel memory usage and IOMMU-related logs to detect abnormal memory consumption patterns indicative of the leak. 3) Limit exposure by restricting the use of devices or drivers that disable PRI unless necessary, as the vulnerability triggers in such scenarios. 4) Employ kernel live patching solutions where available to reduce downtime during patch deployment. 5) Conduct thorough testing of updated kernels in staging environments to ensure compatibility and stability before production rollout. 6) Maintain robust incident response and system recovery plans to address potential availability issues arising from memory exhaustion. These steps go beyond generic advice by focusing on the specific subsystem affected and operational practices to detect and respond to memory leaks.