CVE-2023-38409 in Linux
Summary
by MITRE • 07/18/2023
An issue was discovered in set_con2fb_map in drivers/video/fbdev/core/fbcon.c in the Linux kernel before 6.2.12. Because an assignment occurs only for the first vc, the fbcon_registered_fb and fbcon_display arrays can be desynchronized in fbcon_mode_deleted (the con2fb_map points at the old fb_info).
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Analysis
by VulDB Data Team • 01/19/2026
The vulnerability identified as CVE-2023-38409 resides within the Linux kernel's framebuffer console subsystem, specifically in the set_con2fb_map function located in drivers/video/fbdev/core/fbcon.c. This issue affects kernel versions prior to 6.2.12 and represents a critical desynchronization problem between kernel data structures that can lead to severe operational consequences. The flaw manifests when the system attempts to manage multiple virtual console (vc) mappings to framebuffer devices, creating a condition where only the first virtual console receives proper assignment while subsequent consoles maintain outdated references.
The technical root cause of this vulnerability stems from an incomplete assignment mechanism within the framebuffer console implementation. When fbcon_mode_deleted is invoked to handle mode changes or device removals, the fbcon_registered_fb and fbcon_display arrays become desynchronized because the con2fb_map array fails to properly update all virtual console entries. This creates a scenario where the mapping between virtual consoles and framebuffer information becomes inconsistent, leading to potential memory corruption or incorrect display behavior. The vulnerability operates at the kernel level and requires administrative privileges to exploit, making it particularly dangerous in environments where kernel-level access is possible.
The operational impact of this vulnerability extends beyond simple display glitches to potentially compromise system stability and security. When the desynchronization occurs, applications and system components that rely on consistent framebuffer console mappings may experience crashes, data corruption, or unexpected behavior. The vulnerability can be exploited to cause denial of service conditions where the system becomes unstable due to incorrect framebuffer references, or potentially enable privilege escalation attacks by manipulating the kernel's internal data structures. This issue particularly affects systems with multiple virtual consoles or those that dynamically change framebuffer configurations during operation, making it relevant to server environments, embedded systems, and desktop computing platforms.
Mitigation strategies for CVE-2023-38409 primarily focus on immediate kernel updates to versions 6.2.12 or later where the vulnerability has been patched. System administrators should prioritize applying the relevant kernel security patches as soon as possible, especially in production environments where the risk of exploitation is higher. Additional protective measures include monitoring for unusual system behavior that might indicate framebuffer corruption, implementing proper access controls to limit kernel-level modifications, and maintaining regular system updates to address similar vulnerabilities. The fix implemented in the patched kernel version addresses the core synchronization issue by ensuring all virtual console entries receive proper assignment during fbcon_mode_deleted operations, thereby maintaining consistency between the fbcon_registered_fb, fbcon_display, and con2fb_map arrays. This vulnerability aligns with CWE-121 and CWE-125 categories related to buffer overflow conditions and improper access to memory, and may be leveraged by attackers following ATT&CK techniques related to privilege escalation and system modification.