CVE-2025-21956 is a vulnerability identified in the Linux kernel's AMD GPU driver component, specifically within the drm/amd/display subsystem. The issue arises from improper handling of a specific color depth setting, COLOR_DEPTH_141414 (14 bits per color channel), which is used by certain AMD Radeon graphics cards, notably the RX 6600 XT. The vulnerability manifests as a warning message triggered by the kernel when the display_color_depth equals COLOR_DEPTH_141414, due to the failure to assign a normalized pixel clock (normalized_pix_clk) value correctly. This leads to an unhandled case in the function calculate_phy_pix_clks, resulting in a warning and potentially unstable or incorrect display behavior. The root cause is that the pixel clock calculation did not account for the 14-bit color depth scenario, which is fixed by assigning the pixel clock multiplied by (14 * 3) / 24, aligning it with other color depth calculations. The patch also includes code style improvements such as fixing indentation in the get_norm_pix_clk function. Although this vulnerability does not appear to be exploitable for remote code execution or privilege escalation, it can cause kernel warnings and potentially impact the stability or reliability of the display subsystem on affected hardware. The vulnerability affects Linux kernel versions containing the specified commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and was published on April 1, 2025. There are no known exploits in the wild at this time, and no CVSS score has been assigned.

For European organizations, the impact of CVE-2025-21956 is primarily related to system stability and reliability rather than direct security compromise. Organizations using Linux systems with AMD Radeon RX 6600 XT or similar GPUs in critical infrastructure, workstations, or servers that rely on graphical output may experience kernel warnings or display issues. This could lead to system crashes, degraded performance, or interruptions in services that depend on graphical interfaces, such as digital signage, visualization platforms, or graphical user interfaces in industrial control systems. While the vulnerability does not directly expose systems to data breaches or privilege escalation, the resulting instability could cause operational disruptions or increased maintenance overhead. For sectors such as finance, healthcare, and manufacturing in Europe, where uptime and reliability are critical, even minor kernel-level issues can have cascading effects. Additionally, organizations with strict compliance requirements may need to address this vulnerability promptly to maintain system integrity and avoid audit findings related to unpatched kernel vulnerabilities.

To mitigate the risks associated with CVE-2025-21956, European organizations should: 1) Apply the official Linux kernel patch that addresses the normalized_pix_clk assignment for the 14-bit color depth scenario as soon as it becomes available in their distribution's kernel updates. 2) Prioritize updating Linux systems running AMD Radeon RX 6600 XT or similar GPUs, especially those used in critical environments. 3) Conduct thorough testing of the updated kernel in staging environments to ensure compatibility and stability before deployment in production. 4) Monitor kernel logs for warnings related to drm/amd/display and calculate_phy_pix_clks to detect any residual issues. 5) If immediate patching is not feasible, consider temporarily disabling or avoiding the use of the affected color depth setting (COLOR_DEPTH_141414) if configurable, to prevent triggering the vulnerability. 6) Maintain up-to-date hardware drivers and firmware for AMD GPUs to reduce the risk of related issues. 7) Implement robust system monitoring and alerting to quickly identify and respond to any display subsystem anomalies that could indicate exploitation or system instability.