CVE-2021-47383 is a vulnerability identified in the Linux kernel's framebuffer console (fbcon) subsystem, specifically related to the handling of the FBIOPUT_VSCREENINFO ioctl call. This ioctl is used by userspace programs to set variable screen information via the fb_var_screeninfo structure. The vulnerability arises when the structure passed contains only partial fields (xres, yres, and bits_per_pixel) with values identical to a previous ioctl call. Under these conditions, the kernel's vc_resize() function incorrectly determines that no screen resize is necessary and skips calling resize_screen(). As a result, the fb_var_screeninfo structure remains incomplete. This incomplete data causes the updatescrollmode() function to compute an incorrect value for fbcon_display->vrows, which in turn leads the real_y() function to return an invalid y coordinate. Ultimately, this chain of miscalculations causes the imageblit function to perform an out-of-bound access on vmalloc memory, leading to a potential memory corruption or kernel crash. The patch fixes this by ensuring resize_screen() is called regardless of whether a resize is detected, thus properly initializing and filling the fb_var_screeninfo structure to prevent the out-of-bound access. This vulnerability affects Linux kernel versions prior to the patch date and is related to framebuffer device ioctl handling, a critical component for graphical console operations on Linux systems.

For European organizations, the impact of this vulnerability can be significant, particularly for those relying on Linux-based systems with framebuffer console support, such as embedded devices, industrial control systems, or servers using framebuffer for console output. Exploitation could lead to kernel crashes (denial of service) or potentially enable local privilege escalation if an attacker can manipulate the framebuffer ioctl calls. While remote exploitation is unlikely without local access, compromised or malicious users or processes could exploit this flaw to destabilize systems or escalate privileges. This could disrupt critical infrastructure, manufacturing systems, or enterprise servers running Linux, causing operational downtime and potential data integrity issues. Given the widespread use of Linux in European IT environments, especially in sectors like telecommunications, manufacturing, and government, the vulnerability poses a moderate risk if left unpatched.

European organizations should prioritize patching Linux kernels to the fixed versions that include the resize_screen() call correction. Specifically, kernel updates from May 2024 onward should be applied promptly. For systems where immediate patching is not feasible, restricting access to framebuffer ioctl calls via mandatory access controls (e.g., SELinux, AppArmor) or limiting userspace program permissions can reduce exploitation risk. Additionally, monitoring for unusual ioctl calls or kernel crashes related to framebuffer operations can help detect attempted exploitation. Organizations should also audit embedded and industrial Linux devices that may not receive regular updates and plan for firmware or kernel upgrades. Implementing robust local user privilege management and minimizing the number of users with access to framebuffer device interfaces will further reduce attack surface.