CVE-2026-64387 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix query directory replay double-free
A response-bearing attempt can return a replayable error and free its response buffer. If SMB2_query_directory_init() fails before the next send, cleanup retains the previous buffer type and frees that response again.
Reset response bookkeeping before each attempt to prevent the stale free.
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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 double-free condition can occur during SMB2 query directory operations. The flaw manifests when the smb client attempts to process directory queries and encounters a replayable error scenario. The root cause lies in improper response buffer management where the client frees a response buffer that has already been freed during a previous attempt, creating a dangerous memory corruption state that could be exploited by malicious actors.
The technical implementation issue stems from the SMB2_query_directory_init() function which fails to properly reset response bookkeeping state before attempting subsequent sends. When an error occurs and the system attempts to replay the directory query, the cleanup process retains knowledge of the previous buffer type and proceeds to free memory that has already been deallocated. This creates a classic double-free vulnerability pattern that violates fundamental memory safety principles and can lead to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation attacks within networked environments where SMB clients are actively processing directory queries. Attackers could exploit this condition by crafting malicious SMB responses that trigger the specific error scenario, leading to denial of service conditions or more severe exploitation vectors. The vulnerability affects systems running Linux kernels with SMB client implementations and represents a significant risk in enterprise environments where file sharing protocols are heavily utilized.
This issue aligns with CWE-415 which specifically addresses double free vulnerabilities in memory management operations. From an attack perspective, it maps to techniques described in the MITRE ATT&CK framework under privilege escalation and denial of service tactics. The vulnerability demonstrates poor resource management practices that violate secure coding guidelines for kernel-level programming where memory safety is paramount.
Mitigation strategies include applying the kernel patches that reset response bookkeeping before each attempt to prevent stale free operations, implementing proper buffer lifecycle management during error recovery scenarios, and ensuring that all memory deallocation operations are properly tracked and validated. System administrators should prioritize updating their Linux kernel versions to include the fixed implementation that addresses this specific double-free condition in the SMB client subsystem. Additionally, monitoring network traffic for suspicious SMB query patterns and implementing network segmentation can help reduce the attack surface for potential exploitation attempts targeting this vulnerability.