CVE-2026-80552 in Linux
Summary
by MITRE • 08/26/2026
In the Linux kernel, the following vulnerability has been resolved:
s390/vfio_ccw: Ensure index for read/write regions are within range
The introduction of the capability chain rightly clamped the region indexes to the range of the capabilities itself, but neglected to do so for the existing read/write regions which should also be enforced.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability identified in the Linux kernel's s390 vfio_ccw subsystem represents a critical boundary check failure that allows out-of-bounds memory access through improperly validated region indexes. This issue stems from an incomplete implementation of security controls during the refactoring or enhancement of capability chain handling mechanisms. While developers correctly implemented range clamping for new capability-related regions, they overlooked applying equivalent validation logic to existing read and write operation regions. This inconsistency creates a discrepancy in how input parameters are processed depending on which code path is executed, leading to potential exploitation scenarios where an attacker can manipulate region indices beyond their valid limits.
From a technical perspective, the flaw resides within the device driver interface for IBM System z channel I/O operations managed via VFIO (Virtual Function I/O). The vfio_ccw component facilitates direct assignment of hardware devices to virtual machines or containers by exposing specific kernel interfaces to user-space applications. When these applications issue commands involving read or write regions, the kernel must ensure that all referenced memory indices fall within pre-allocated and validated boundaries. By failing to clamp these indexes for existing regions, the system permits access to arbitrary physical or virtual memory locations outside the intended scope of the device's operational context. This bypasses essential isolation guarantees provided by the VFIO framework, potentially allowing unauthorized data exfiltration or modification of kernel structures adjacent to the targeted buffers.
The operational impact of this vulnerability is severe due to its potential for privilege escalation and system compromise. An unprivileged user-space process interacting with a vfio_ccw device could craft malicious requests that specify out-of-bounds region indexes. If successful, such exploitation enables arbitrary read or write operations within kernel space memory. This capability can be leveraged to overwrite critical data structures, inject code execution payloads, or extract sensitive information from the host system. In virtualized environments, this breach undermines the security boundary between guest instances and the underlying hypervisor infrastructure, potentially leading to cross-tenant attacks if multiple tenants share the same physical hardware resources managed by vulnerable kernel modules.
This vulnerability aligns with CWE-125, Out-of-bounds Read, and CWE-787, Out-of-bounds Write, as it involves accessing memory locations beyond allocated boundaries due to insufficient input validation. In terms of offensive security frameworks, this flaw supports techniques categorized under ATT&CK T1055, Process Injection, or more broadly within Privilege Escalation vectors where kernel-level access is achieved through driver vulnerabilities. The root cause reflects a common pattern in software development known as incomplete mitigation during incremental updates, where new features are secured but legacy code paths remain unprotected against similar attack vectors.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that addresses this specific oversight by extending index validation logic to cover all relevant region types uniformly. System administrators should ensure their systems run patched versions of the s390 vfio_ccw driver and monitor for updates from distribution vendors who backport these fixes to stable releases. For environments where immediate patching is not feasible, restricting access to VFIO devices through strict MAC policies or disabling unnecessary device assignments can reduce the attack surface. Additionally, implementing runtime monitoring tools that detect anomalous memory access patterns in kernel modules may provide early warning indicators of exploitation attempts targeting this class of boundary check failures.