CVE-2026-80786 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
fbdev: Wrap user-invoked calls to fb_set_var() in helper
Handle fbcon during display updates in fb_set_var_from_user(). Check with fbcon if the mode change is possible, update hardware state and finally update fbcon. Update all callers.
Only the FBIOPUT_VSCREENINFO ioctl currently does all steps. Other mode-changes callers in sysfs and driver code are missing fbcon-related steps.
With the new helper, ps3fb and sh_mobile_lcdcfb no longer maintain fbcon state themselves.
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Analysis
by VulDB Data Team • 09/05/2026
The Linux kernel framebuffer subsystem contained a structural inconsistency in how display configuration changes were propagated to the console layer. Specifically, while the FBIOPUT_VSCREENINFO ioctl handler correctly invoked the necessary helper functions to synchronize hardware state with the virtual terminal and framebuffer console (fbcon) layers, other code paths that modified video mode parameters via sysfs attributes or direct driver calls did not perform these critical synchronization steps. This discrepancy arose because various kernel components directly manipulated framebuffer variables without ensuring that the fbcon subsystem was notified of potential changes in resolution, color depth, or screen geometry. The absence of a unified entry point for user-invoked configuration updates meant that certain drivers maintained their own fragile and often incomplete logic to handle console state transitions, leading to divergent behavior depending on how the display settings were altered.
This architectural flaw resulted in scenarios where hardware registers could be updated with new video modes while the fbcon layer remained unaware of the transition or failed to reconfigure its internal data structures accordingly. Such desynchronization typically manifests as visual artifacts including screen corruption, frozen displays, or complete loss of console output after a mode change is initiated through non-ioctl interfaces like sysfs entries. In some cases, accessing invalid memory regions within the framebuffer mapping could occur if fbcon continued to operate under assumptions about buffer layouts that no longer matched the hardware configuration. These issues were particularly prevalent in drivers such as ps3fb and sh_mobile_lcdcfb, which previously implemented their own ad-hoc mechanisms for managing fbcon state updates during mode changes, increasing code complexity and the likelihood of synchronization errors due to duplicated logic across multiple driver implementations.
The resolution involves wrapping all user-invoked calls to fb_set_var within a dedicated helper function named fb_set_var_from_user that enforces a strict operational sequence: first consulting fbcon to validate whether the requested mode change is permissible, then updating the hardware state accordingly, and finally notifying fbcon of the successful transition. This refactoring ensures consistent behavior regardless of the interface used to trigger display updates, effectively centralizing the validation and synchronization logic. By standardizing this workflow, drivers no longer need to maintain separate code paths for handling console notifications during mode changes, thereby reducing maintenance burden and eliminating race conditions or state mismatches between the hardware abstraction layer and the virtual terminal subsystem.
From a vulnerability classification perspective, this issue aligns with CWE-20 Improper Input Validation as it relates to insufficient checks before modifying system resources, although its primary impact is stability rather than security exploitation in most contexts. It also touches upon CWE-665 Improper Initialization since prior implementations failed to properly initialize or synchronize state across subsystem boundaries during configuration changes. In terms of the MITRE ATT&CK framework, while not a direct attack vector for privilege escalation, such inconsistencies can contribute to Denial of Service conditions by causing kernel panics or unresponsive systems when triggered repeatedly through sysfs interfaces. Mitigation strategies include applying the upstream kernel patch that introduces fb_set_var_from_user and ensuring all driver callers are updated to use this standardized helper instead of directly invoking lower-level set operations without console synchronization. System administrators should monitor for display instability after configuration changes and ensure their kernels are patched to version containing this fix, particularly if they utilize sysfs-based tools for dynamic screen resolution adjustments or remote management interfaces that modify framebuffer parameters programmatically.