CVE-2018-8781 in Linux
Summary
by MITRE
The udl_fb_mmap function in drivers/gpu/drm/udl/udl_fb.c at the Linux kernel version 3.4 and up to and including 4.15 has an integer-overflow vulnerability allowing local users with access to the udldrmfb driver to obtain full read and write permissions on kernel physical pages, resulting in a code execution in kernel space.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2018-8781 resides within the Linux kernel's udl framebuffer driver implementation, specifically in the udl_fb_mmap function located at drivers/gpu/drm/udl/udl_fb.c. This flaw affects kernel versions ranging from 3.4 through 4.15, representing a significant attack surface across multiple long-term support releases. The udl driver is designed to support USB DisplayLink devices, enabling graphics output through usb connections, making it a common component in various embedded systems and desktop environments where such hardware is utilized. The vulnerability stems from inadequate input validation and arithmetic handling within the memory mapping function that processes framebuffer memory requests from user-space applications.
The technical nature of this vulnerability manifests as an integer overflow condition that occurs when the udl_fb_mmap function processes memory mapping requests for the framebuffer device. When local users with access to the udldrmfb driver invoke memory mapping operations, the function fails to properly validate or clamp integer values that determine the size and offset of memory regions being mapped. This overflow condition allows attackers to manipulate the memory mapping parameters in such a way that they can bypass normal memory access restrictions and gain direct access to kernel physical memory pages. The vulnerability specifically enables attackers to obtain full read and write permissions on kernel physical pages, which represents a critical escalation from user-space to kernel-space privileges.
The operational impact of this vulnerability is severe and far-reaching, as it provides local attackers with the capability to execute arbitrary code within kernel space with the highest possible privileges. This privilege escalation allows attackers to bypass all kernel security mechanisms, including memory protection, access controls, and security modules that typically prevent user-space processes from directly accessing kernel memory. The implications extend beyond simple code execution to include complete system compromise, data exfiltration, and potential persistence mechanisms within the kernel space. Attackers can leverage this vulnerability to modify kernel data structures, inject malicious code into kernel memory, or even disable security features such as kernel address space layout randomization and memory management protections.
This vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and represents a classic example of how improper integer handling can lead to privilege escalation in kernel space. From an attacker's perspective, the vulnerability maps to ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation," and T1059, covering "Command and Scripting Interpreter," as the compromised kernel access enables full system control. The exploitability of this vulnerability is relatively straightforward for local attackers who already have access to the udldrmfb driver, making it particularly dangerous in environments where such drivers are exposed to untrusted users or where privilege separation is insufficient.
Mitigation strategies for CVE-2018-8781 should focus on immediate kernel updates to versions that contain the patched udl_fb_mmap function with proper integer overflow protections. System administrators should also implement strict access controls to prevent unauthorized users from accessing the udldrmfb driver interface, which includes reviewing udev rules and device permissions. Additional protective measures include enabling kernel security features such as kernel page table isolation, disabling unnecessary USB DisplayLink support when not required, and implementing monitoring solutions that can detect anomalous memory mapping activities. Organizations should also consider implementing automated patch management systems to ensure all affected kernel versions are promptly updated, as this vulnerability affects a wide range of supported kernel releases that may still be in active use across various deployments.