CVE-2026-64381 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: Fix next buffer leak in receive_encrypted_standard()
receive_encrypted_standard() allocates next_buffer before checking whether the number of compound PDUs already reached MAX_COMPOUND. If the limit check fails, the function returns immediately and the newly allocated next_buffer is not assigned to server->smallbuf/server->bigbuf, making it leaked.
Move the MAX_COMPOUND check before allocating next_buffer.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists within the Linux kernel's SMB client implementation where a memory leak occurs in the receive_encrypted_standard() function. The flaw represents a classic resource management issue that can lead to progressive memory consumption and potential system instability. The vulnerability is classified as a buffer management error that directly impacts the kernel's ability to properly handle network protocol communications.
The technical execution of this vulnerability occurs when the SMB client processes encrypted standard responses from servers. During this process, the function attempts to allocate memory for next_buffer before validating whether the maximum compound PDU limit has been reached. This ordering issue creates a scenario where allocated memory becomes orphaned when the MAX_COMPOUND validation fails and the function exits prematurely. The allocated next_buffer is never properly assigned to either server->smallbuf or server->bigbuf, resulting in a memory leak that persists until the system reboots or the memory is reclaimed through other means.
The operational impact of this vulnerability extends beyond simple memory consumption as it represents a potential denial of service vector within networked systems. When exploited repeatedly, particularly in environments with high SMB traffic volumes, the cumulative effect of leaked buffers can degrade system performance significantly. The vulnerability affects systems running Linux kernels that implement SMB client functionality and could be particularly problematic in server environments where sustained network communication is expected. Attackers could potentially leverage this weakness to exhaust available memory resources, leading to system instability or complete service unavailability.
This issue aligns with CWE-401 which specifically addresses memory leaks in software implementations and demonstrates poor resource management practices within kernel code. The vulnerability also intersects with ATT&CK technique T1499.004 which involves network denial of service attacks through resource exhaustion. The fix implemented moves the MAX_COMPOUND validation check before buffer allocation, ensuring proper resource management flow and preventing the premature allocation of memory that would otherwise be leaked. This remediation approach follows standard security practices for preventing resource leaks in kernel-space code and aligns with best practices for maintaining system stability under high network load conditions.
The vulnerability highlights the importance of careful ordering in resource management within kernel modules, particularly when dealing with protocol parsing functions that must handle variable-length data structures. Proper initialization and validation sequences are essential to prevent such memory leak scenarios where allocated resources become inaccessible due to early function exits. The fix represents a fundamental correction to the control flow logic that ensures all allocated resources are properly accounted for regardless of execution path taken during protocol handling operations.
Security practitioners should prioritize this vulnerability for remediation in production environments, particularly those with high SMB traffic volumes or critical network infrastructure dependencies. Regular kernel updates and security patch management procedures should include verification of SMB client implementations to ensure proper memory management practices are maintained. The vulnerability serves as a reminder of the critical importance of thorough testing and validation of resource allocation sequences within kernel modules where memory leaks can have system-wide implications rather than just application-level consequences.