CVE-2021-47087 is a vulnerability identified in the Linux kernel specifically related to the Trusted Execution Environment (TEE) subsystem, more precisely the OP-TEE (Open Portable Trusted Execution Environment) driver. The issue arises from an incorrect handling of memory page pointers during the freeing process. In the vulnerable code, the pointer to the allocated memory pages (struct page *page) is advanced or modified before the call to __free_pages(page, order). This results in the kernel potentially freeing arbitrary pages of memory rather than the intended allocated pages. Such incorrect memory management can lead to undefined behavior including memory corruption, use-after-free conditions, or kernel crashes. The root cause is that the pointer is incremented or moved forward during allocation, and the freeing function is called on this modified pointer rather than the original base pointer, which violates the expected contract of __free_pages. The fix involves ensuring that the page pointer is not modified before passing it to __free_pages, thereby preventing accidental freeing of unintended memory regions. This vulnerability is present in certain Linux kernel versions identified by specific commit hashes, and it has been publicly disclosed and patched as of March 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, the impact of this vulnerability can be significant depending on their use of Linux systems that include the OP-TEE driver, which is commonly used in embedded systems, mobile devices, and some specialized hardware requiring secure execution environments. Exploitation could lead to kernel memory corruption, causing system instability, denial of service (system crashes), or potentially privilege escalation if an attacker can manipulate kernel memory. This could compromise the confidentiality and integrity of sensitive data processed within the trusted execution environment. Organizations relying on Linux-based infrastructure, especially those in sectors such as telecommunications, automotive, industrial control, and IoT devices, may be at risk. The lack of known exploits suggests a lower immediate threat, but the vulnerability’s nature means that once exploited, it could be leveraged for advanced persistent threats or targeted attacks. The impact on availability is also notable, as kernel crashes can disrupt critical services. Given the kernel-level nature, remediation requires patching the kernel, which may involve downtime or complex update procedures.

European organizations should prioritize patching affected Linux kernel versions with the updated code that corrects the page pointer handling in the OP-TEE driver. Since this vulnerability involves kernel memory management, applying vendor-supplied kernel updates or backported patches is critical. Organizations using embedded or specialized Linux distributions should coordinate with their vendors to obtain timely patches. Additionally, they should audit their systems to identify devices running vulnerable kernel versions, especially those employing OP-TEE or similar trusted execution environments. Employing kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), strict memory protection policies, and enabling kernel lockdown modes can reduce exploitation risk. Monitoring system logs for unusual kernel errors or crashes may help detect attempted exploitation. For environments where immediate patching is not feasible, isolating vulnerable systems and limiting access to trusted users can reduce exposure. Finally, organizations should maintain an inventory of Linux kernel versions in use and implement a robust patch management process to respond quickly to such vulnerabilities.