CVE-2026-80582 in Linux
Summary
by MITRE • 08/26/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/shmem_helper: Check VMA boundaries for PMD mappings
In the ->huge_fault handler do not install a PMD huge page mapping if the huge page exceeds the boundaries of the VMA.
All other ->huge_fault handlers have similar checks and the resulting mapping will trigger a VM_BUG_ON_VMA() if it ever reaches copy_pmd_range().
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Analysis
by VulDB Data Team • 08/26/2026
The Linux kernel's Direct Rendering Manager subsystem, specifically within the shared memory helper component responsible for handling graphics buffer objects backed by system RAM, contained a logic flaw in its huge page fault handler. This handler is invoked when the kernel attempts to map large pages into a process virtual address space to optimize performance and reduce translation lookaside buffer pressure. The specific vulnerability arises because the implementation failed to validate whether the requested Page Middle Directory mapping would extend beyond the defined boundaries of the Virtual Memory Area associated with the memory region. While other handlers within the same subsystem correctly enforced these boundary checks, this particular handler omitted the necessary validation step, creating an inconsistency in how virtual memory mappings are constructed and managed across different drivers using shared memory helpers.
From a technical perspective, this oversight allows for the installation of a PMD huge page mapping that overlaps with unmapped or invalid regions outside the intended VMA limits. Under normal operation, such an out-of-bounds mapping would eventually trigger a VM_BUG_ON_VMA assertion when the kernel attempts to copy the Page Middle Directory range during subsequent memory operations. This assertion is designed as a safety mechanism to catch programming errors in the kernel's virtual memory management code by causing a kernel panic or crash if invalid state is detected. However, relying on this late-stage detection rather than preventing the invalid mapping at the point of creation represents a significant architectural weakness that can lead to system instability and denial of service conditions without requiring any specific exploitation beyond triggering the fault path under certain memory allocation scenarios.
The operational impact of this vulnerability primarily centers around system stability and availability. An attacker or malicious process could potentially trigger this code path by allocating large graphics buffers and causing page faults that require huge page mappings, thereby inducing a kernel panic through the triggered VM_BUG_ON_VMA assertion. This results in an immediate denial of service for all users on the affected system as the kernel halts execution to prevent further corruption or undefined behavior. In environments where graphical processing is critical, such as desktop systems or servers running GPU-accelerated workloads, this vulnerability poses a tangible risk to uptime and reliability. The lack of boundary checks means that valid-looking requests can result in invalid memory states being committed before the kernel's internal consistency checks catch them.
This issue aligns with CWE-787 Out-of-bounds Write vulnerabilities where data is written beyond the intended buffer or memory region, leading to potential system crashes or corruption. In terms of attack vectors and techniques, it relates to ATT&CK technique T1499 Endpoint Denial of Service, as exploiting this flaw allows an entity to crash the operating system kernel by triggering a fatal assertion error within core subsystems. Mitigation for this vulnerability involves applying the upstream Linux kernel patch that adds explicit boundary checks in the ->huge_fault handler for drm/shmem_helper drivers. System administrators should ensure their systems are updated with kernels containing this fix, which enforces consistency across all huge page fault handlers by verifying that any proposed PMD mapping remains strictly within the VMA limits before installation. Regularly updating kernel packages and monitoring for vendor security advisories related to graphics subsystems is essential to maintaining system integrity against such memory management flaws.