Overview
CVE-2025-40266 describes a vulnerability in the Kernel-based Virtual Machine (KVM) subsystem of the Linux kernel, specifically affecting the arm64 architecture. This vulnerability is related to the handling of FF-A (Firmware Framework for Arm) memory sharing between the host kernel and guest VMs. The issue could potentially allow a malicious host to trigger an out-of-bounds (OOB) access in the hypervisor by providing a specially crafted offset value.
Technical Details
The vulnerability stems from insufficient validation of the offset used to access the FF-A buffer. The host kernel can specify an offset value. If this offset is a large enough value (specifically, in the range [U32_MAX – sizeof(struct ffa_composite_mem_region) + 1, U32_MAX]), it can lead to an out-of-bounds read or write when the hypervisor attempts to access the memory region.
The vulnerable code path involves the processing of ffa_composite_mem_region structures. Without proper bounds checking on the offset, an attacker-controlled value could bypass security checks and cause the hypervisor to access memory outside the allocated buffer.
CVSS Analysis
Currently, the CVE entry lists the severity as N/A and the CVSS score as N/A. This likely indicates that a CVSS score hasn’t been formally calculated yet, or the impact is still being assessed. However, given that the vulnerability could lead to an out-of-bounds access in the hypervisor, it has the potential to be rated as at least a medium severity, and could potentially be higher if it leads to code execution. A potential attacker controlled the offset value, and potentially control hypervisor memory access.
Possible Impact
The primary impact of this vulnerability is the potential for information disclosure or denial-of-service (DoS). An out-of-bounds read could expose sensitive data from the hypervisor’s memory space. An out-of-bounds write, although less likely given the context, could corrupt hypervisor data structures, leading to system instability or a crash. Depending on the specific memory region accessed, it’s theoretically possible that this vulnerability could be leveraged for more serious exploits, potentially leading to guest-to-host escape.
Mitigation or Patch Steps
The vulnerability has been addressed in the Linux kernel. Users are strongly advised to update their kernels to a patched version. The fix involves adding proper validation to the offset value before accessing the FF-A buffer. This ensures that the offset remains within the bounds of the allocated memory region.
The specific commits that address this vulnerability are:
References
- CVE ID: CVE-2025-40266
- Published: 2025-12-04T16:16:20.787
- Kernel Commit 1
- Kernel Commit 2
- Kernel Commit 3
- Kernel Commit 4
