CVE-2025-21987 in Linux
Summary
by MITRE • 04/02/2025
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: init return value in amdgpu_ttm_clear_buffer
Otherwise an uninitialized value can be returned if amdgpu_res_cleared returns true for all regions.
Possibly closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3812
(cherry picked from commit 7c62aacc3b452f73a1284198c81551035fac6d71)
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Analysis
by VulDB Data Team • 02/16/2026
The vulnerability identified as CVE-2025-21987 resides within the Linux kernel's AMD GPU driver component, specifically in the drm/amdgpu subsystem. This issue affects the amdgpu_ttm_clear_buffer function where a critical initialization oversight occurs in the return value handling. The flaw manifests when the amdgpu_res_cleared function evaluates to true across all memory regions, leading to the return of an uninitialized variable that contains arbitrary data from memory. This represents a classic case of uninitialized memory access that can potentially expose sensitive information or create unpredictable behavior in the graphics driver stack. The vulnerability was tracked in the freedesktop.org drm/amd project under issue #3812 and has been addressed through a targeted code fix that ensures proper initialization of the return value before being passed back to calling functions. The issue demonstrates a fundamental coding error that violates secure programming practices and could potentially be exploited to extract information from kernel memory space.
The technical implementation flaw stems from the amdgpu_ttm_clear_buffer function failing to initialize its return value variable before processing the results of amdgpu_res_cleared checks across multiple memory regions. When all regions return true from the clearing operation, the function proceeds to return without setting the return value to a proper initialized state, leaving whatever garbage data was previously present in that memory location to be interpreted as the function's result. This uninitialized return value can contain sensitive information from kernel memory, potentially exposing system state or configuration details to unauthorized access. The flaw operates at the kernel level where memory management and graphics processing intersect, making it particularly concerning as it affects the fundamental graphics subsystem that handles memory allocation and buffer management for GPU operations. This vulnerability directly corresponds to CWE-457: Use of Uninitialized Variable, which is classified as a medium severity issue in the Common Weakness Enumeration catalog and represents a well-known class of vulnerabilities that can lead to information disclosure or system instability.
The operational impact of this vulnerability extends beyond simple information leakage, as it can potentially enable attackers to gain insights into kernel memory layout and state information that could be leveraged in more sophisticated attacks. While the immediate risk may appear limited to returning uninitialized data rather than executing arbitrary code, the exposure of kernel memory contents can provide attackers with valuable information for crafting targeted exploits. The vulnerability affects systems running Linux kernels with AMD GPU drivers, particularly those utilizing the ttm (Translation Table Manager) subsystem for memory management. Attackers could potentially use this information to understand memory patterns, identify system configurations, or develop more effective exploitation techniques against other vulnerabilities present in the same kernel subsystem. The fix implemented addresses the core issue by ensuring proper initialization of the return value before any conditional logic determines the final result, preventing the leakage of uninitialized memory contents.
Mitigation strategies for this vulnerability should focus on applying the kernel update that includes the fix for CVE-2025-21987, which properly initializes the return value in the amdgpu_ttm_clear_buffer function. System administrators should prioritize patching affected systems, particularly those running Linux kernels with AMD GPU support, as the vulnerability exists at the kernel level where it can impact the entire system security posture. The fix aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation by preventing information disclosure that could be used to facilitate more advanced attacks. Organizations should also implement monitoring for unusual memory access patterns or kernel behavior that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper initialization in kernel code and highlights the need for comprehensive testing of memory management functions that handle sensitive data. Security teams should consider this vulnerability as part of broader kernel security hardening efforts, particularly in environments where AMD GPU hardware is deployed and where information disclosure risks are particularly concerning. Regular kernel updates and security audits remain crucial for maintaining system integrity and preventing exploitation of similar uninitialized variable issues in other kernel subsystems.