CVE-2025-38702 in Linux
Summary
by MITRE • 09/04/2025
In the Linux kernel, the following vulnerability has been resolved:
fbdev: fix potential buffer overflow in do_register_framebuffer()
The current implementation may lead to buffer overflow when: 1. Unregistration creates NULL gaps in registered_fb[]
2. All array slots become occupied despite num_registered_fb < FB_MAX 3. The registration loop exceeds array bounds
Add boundary check to prevent registered_fb[FB_MAX] access.
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Analysis
by VulDB Data Team • 02/10/2026
The vulnerability described in CVE-2025-38702 represents a critical buffer overflow condition within the Linux kernel's frame buffer subsystem that specifically affects the do_register_framebuffer() function. This flaw exists in the fbdev driver component responsible for managing frame buffer devices and their registration within the kernel's internal data structures. The vulnerability manifests when the kernel attempts to register frame buffer devices and encounters specific conditions that lead to memory corruption through improper bounds checking. The root cause lies in the kernel's handling of the registered_fb[] array which serves as the primary registry for active frame buffer devices, where the implementation fails to properly validate array boundaries during device registration operations.
The technical implementation flaw occurs when the kernel's frame buffer registration mechanism encounters situations where NULL gaps are created within the registered_fb[] array during device unregistration processes. This creates a scenario where the num_registered_fb counter may not accurately reflect the actual occupied slots in the array, leading to a condition where all available array slots become filled despite the num_registered_fb value remaining below the FB_MAX threshold. The vulnerability is particularly insidious because it operates under the assumption that the array indices will always align with the registered device count, creating a mismatch between the logical device tracking and the physical array management. When the registration loop attempts to access memory locations beyond the intended array bounds, specifically targeting registered_fb[FB_MAX], the kernel experiences a buffer overflow that can result in arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a potential privilege escalation vector that could allow malicious actors to execute code with kernel-level privileges. The buffer overflow condition creates opportunities for attackers to manipulate kernel memory structures and potentially gain unauthorized access to system resources. This vulnerability directly impacts the stability and security of Linux systems that utilize frame buffer devices, particularly those running kernel versions containing the affected code. The flaw affects systems where multiple frame buffer devices are registered and unregistered dynamically, making it relevant to embedded systems, servers with graphics capabilities, and any environment where the kernel's frame buffer subsystem is actively utilized. According to CWE classification, this vulnerability maps to CWE-121: Stack-based Buffer Overflow, while ATT&CK framework categorizes it under T1068: Exploitation for Privilege Escalation and T1547: Boot or Logon Autostart Execution, highlighting its potential for system compromise and persistence mechanisms.
Mitigation strategies for CVE-2025-38702 require immediate kernel updates from vendors who have patched the buffer overflow condition in their frame buffer implementations. System administrators should prioritize patching operations, particularly in environments where frame buffer devices are actively used or where the system's security posture depends on kernel integrity. The fix involves implementing proper boundary checks that prevent access to registered_fb[FB_MAX] and ensure that all array accesses remain within valid memory boundaries. Additional defensive measures include monitoring for unusual frame buffer registration patterns, implementing kernel address space layout randomization where applicable, and maintaining strict access controls for systems that handle graphics processing. The vulnerability also underscores the importance of comprehensive kernel security testing, particularly for subsystems that manage device registration and memory allocation, as similar buffer overflow conditions may exist in other kernel components. Organizations should also consider implementing intrusion detection systems that can monitor for anomalous kernel memory access patterns that might indicate exploitation attempts targeting this or similar vulnerabilities.