CVE-2026-64368 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
mm/slab: do not limit zeroing to orig_size when only red zoning is enabled
When init (zeroing) on allocation is requested, for kmalloc() we generally have to zero the full object size even if a smaller size is requested, in order to provide krealloc()'s __GFP_ZERO guarantees.
But if we track the requested size, krealloc() uses that information to do the right thing, so we can zero only the requested size. With red zoning also enabled, any extra size became part of the red zone, so it must not be zeroed and thus we must zero only the requested size.
However the current check is imprecise, and will trigger also when only SLAB_RED_ZONE is enabled without SLAB_STORE_USER (which enables tracking the requested size). This means enabling red zoning alone can compromise krealloc()'s __GFP_ZERO contract.
Fix this by using slub_debug_orig_size() instead, which is the exact check for whether the requested size is tracked. We don't need to care if red zoning is also enabled or not. Also update and expand the comment accordingly.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists in the linux kernel's memory management subsystem specifically within the slab allocator implementation. The issue stems from an imprecise conditional check that determines when memory objects should be zeroed during allocation operations. When the kernel allocates memory through kmalloc() with zeroing requirements, it must ensure proper initialization of allocated objects to maintain data integrity and prevent information leakage. The current implementation incorrectly applies zeroing logic based on red zoning flags alone rather than tracking the actual requested size, creating a potential security risk when only red zoning is enabled without user tracking.
The technical flaw manifests in how the kernel handles memory allocation requests that require zero initialization. In normal operation, when kmalloc() is called with __GFP_ZERO flag, it must ensure the entire allocated object is zeroed to maintain consistency with krealloc() behavior. However, when only SLAB_RED_ZONE is enabled without SLAB_STORE_USER, the current code fails to distinguish between these conditions properly. This leads to situations where memory objects are zeroed beyond their requested size, potentially compromising the __GFP_ZERO contract that krealloc() relies on for maintaining consistent memory state. The vulnerability directly impacts the kernel's memory safety mechanisms and can lead to information disclosure or unexpected behavior in memory operations.
The operational impact of this vulnerability extends beyond simple memory management concerns into broader security implications for linux systems. When red zoning is enabled alone without user tracking, the imprecise zeroing logic can cause data from previous allocations to persist in memory regions that should be properly initialized. This creates potential information leakage scenarios where sensitive data might remain accessible through improper memory initialization. The issue affects systems running linux kernels with slab allocator configurations that enable red zoning but not user tracking, potentially compromising system integrity and confidentiality. Attackers could theoretically exploit this weakness to gain insights into previously allocated memory contents or manipulate memory state in unexpected ways.
The fix implemented addresses this vulnerability by replacing the imprecise conditional check with slub_debug_orig_size(), which provides the exact determination of whether the requested size is being tracked. This approach eliminates the dependency on red zoning flags alone and correctly identifies when size tracking information is available for proper zeroing decisions. The solution aligns with established security practices by ensuring that memory allocation guarantees are maintained regardless of configuration settings. Additionally, the accompanying comment updates provide clearer documentation about when zeroing operations should occur, helping prevent similar issues in future implementations and maintaining consistency with industry standards for kernel memory management.
This vulnerability relates to CWE-125 out-of-bounds read and CWE-787 out-of-bounds write conditions that can occur due to improper memory initialization. The fix demonstrates proper implementation of memory safety principles as outlined in the ATT&CK framework's system binary exploitation techniques, specifically addressing memory corruption vulnerabilities through precise conditional logic. The remediation approach ensures proper kernel memory management while maintaining backward compatibility with existing allocation patterns and preserving the intended security guarantees of the __GFP_ZERO flag for user-space applications relying on consistent memory initialization behavior.