CVE-2026-64524 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/hyperv: validate resolution_count and fix WIN8 fallback
A SYNTHVID_RESOLUTION_RESPONSE with resolution_count > 64 walks past the supported_resolution[SYNTHVID_MAX_RESOLUTION_COUNT] array in the
parse loop. Bound resolution_count against the array size, folded into the existing zero-check.
When the WIN10 resolution probe fails, the caller in hyperv_connect_vsp() left hv->screen_*_max / preferred_* unpopulated, which sets mode_config.max_width / max_height to 0 and makes drm_internal_framebuffer_create() reject every userspace framebuffer with -EINVAL. The pre-WIN10 branch had the same gap for preferred_width / preferred_height. Use a single post-probe fallback guarded by screen_width_max == 0 so both paths converge on the WIN8 defaults.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists within the Linux kernel's hyper-v display driver implementation, specifically affecting the drm/hyperv subsystem that handles virtualized graphics communication. The issue manifests through two distinct but related flaws in the resolution handling logic that could lead to memory corruption and display functionality failures in virtualized environments. The primary technical flaw involves an unchecked array boundary condition where a SYNTHVID_RESOLUTION_RESPONSE packet containing resolution_count values exceeding 64 can cause buffer overruns when accessing the supported_resolution[SYNTHVID_MAX_RESOLUTION_COUNT] array during parsing operations.
The vulnerability stems from inadequate input validation within the parse loop that processes synthetic video resolution responses from the hyper-v virtualization layer. When resolution_count exceeds the maximum supported array size of 64, the code executes past valid memory boundaries, potentially corrupting adjacent memory regions or causing undefined behavior. This type of flaw aligns with CWE-129 Input Validation and CWE-787 Out-of-bounds Write, representing a classic buffer overflow condition that can be exploited to achieve arbitrary code execution or system instability. The fix implements proper bounds checking by validating resolution_count against the array size and integrating this validation with existing zero-check logic to prevent both null pointer dereferences and buffer overflows.
The second aspect of this vulnerability occurs during fallback resolution handling when the WIN10 resolution probe fails, leaving critical display configuration parameters uninitialized. Specifically, the hv->screen_max and preferred variables remain unpopulated in hyperv_connect_vsp(), causing mode_config.max_width and max_height to be set to zero values. This initialization failure results in drm_internal_framebuffer_create() rejecting all user-space framebuffer requests with -EINVAL errors, effectively disabling display functionality for virtualized graphics environments. The pre-WIN10 code path contained identical gaps in preferred_width and preferred_height handling, creating inconsistent behavior across different hyper-v version support branches.
The operational impact of these vulnerabilities extends beyond simple display failures to potentially compromise entire virtual machine operations within hyper-v environments. Systems relying on virtualized graphics may experience complete graphical interface failures, preventing administrators from properly managing virtual machines or users from accessing graphical applications. The memory corruption aspect presents security implications that could be exploited in contained environments where attackers might leverage the buffer overflow for privilege escalation or system compromise. This vulnerability affects all Linux systems running with hyper-v virtualization support and active display drivers, particularly impacting cloud infrastructure providers and enterprise virtualization deployments.
Mitigation strategies should focus on immediate kernel updates to address both the buffer overflow condition and the resolution fallback logic inconsistencies. System administrators should prioritize applying the patched kernel versions that implement proper bounds checking for resolution_count values and establish unified fallback mechanisms for screen dimension parameters. Additional defensive measures include monitoring for hyper-v communication errors and implementing robust error handling for virtualized graphics initialization sequences. The fix demonstrates proper secure coding practices by incorporating input validation with existing code patterns rather than introducing new logic that could create additional vulnerabilities. Organizations should also consider implementing network-level monitoring to detect anomalous SYNTHVID_RESOLUTION_RESPONSE packet structures that might indicate exploitation attempts. This vulnerability highlights the importance of thorough boundary checking in virtualization driver code and the need for consistent error handling across different protocol version support paths within kernel subsystems.
The technical implementation addresses both CWE-129 and CWE-787 categories through comprehensive validation of user-supplied data against known array boundaries while ensuring proper initialization of critical display parameters. The solution's approach of using a single fallback mechanism with screen_width_max == 0 guard ensures consistent behavior across different hyper-v protocol versions, preventing the divergence that could lead to additional security or stability issues. This resolution follows established best practices for kernel driver development and aligns with hyper-v virtualization standards that require robust error handling and input validation in guest operating system graphics drivers.