The Linux kernel vulnerability CVE-2026-64524 involves the drm/hyperv driver where SYNTHVID_RESOLUTION_RESPONSE messages with a resolution_count greater than 64 could cause out-of-bounds access of the supported_resolution array. This was due to missing validation of resolution_count against SYNTHVID_MAX_RESOLUTION_COUNT. Additionally, the fallback logic for screen resolution probing on Windows 8 and Windows 10 was flawed, causing uninitialized screen dimension variables and rejection of user-space framebuffer creation with -EINVAL errors. The fix bounds resolution_count and consolidates fallback handling to use WIN8 defaults when WIN10 probing fails. This vulnerability affects Linux kernel versions prior to 7.0.0-28.28 and related variants. The issue is patched in updated kernel releases as per Ubuntu security advisories USN-8618-1 and USN-8663-1.

An attacker could exploit this vulnerability to cause denial of service by preventing framebuffer creation, impacting graphical display functionality. The CVSS vector indicates local attack vector with low complexity and no privileges required, resulting in high confidentiality impact and high availability impact but no integrity impact. There are no known exploits in the wild. The vulnerability could disrupt normal operation of the drm/hyperv subsystem on affected Linux kernel versions.

A patch is available and has been released by Ubuntu in updated Linux kernel packages. Users should apply the kernel updates to versions 7.0.0-28.28 or later as provided in the Ubuntu security notices USN-8618-1 and USN-8663-1. After updating, a system reboot is required. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be necessary. No additional mitigation actions are required beyond applying the official patches.