CVE-2026-64386 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix query_info() replay double-free
A response-bearing attempt can return a replayable error and free its response buffer. If SMB2_query_info_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 resides within the Linux kernel's smb client implementation where a double-free condition can occur during SMB2 query information operations. The flaw manifests when the smb client attempts to query file or directory information through the SMB protocol, specifically in the query_info() function that handles response processing and cleanup operations. The issue stems from improper handling of response buffer management during error conditions, creating a scenario where memory deallocation occurs twice on the same buffer reference.
The technical root cause involves the smb2_query_info_init() function which initializes query information requests before sending them over the network. When this initialization fails or encounters an error condition prior to actual transmission, the cleanup code path attempts to free response buffers without properly resetting the internal bookkeeping state. This results in a stale reference being maintained in the response tracking structures, leading to a second free operation on memory that has already been deallocated. The vulnerability is particularly dangerous because it can lead to memory corruption that may be exploited for privilege escalation or system compromise.
The operational impact of this vulnerability extends beyond simple memory management issues as it affects the stability and security of systems relying on SMB file sharing protocols. When triggered, the double-free condition can cause kernel panics, system crashes, or potentially allow attackers to manipulate memory layout through controlled buffer overflows. The vulnerability is particularly concerning in enterprise environments where SMB servers are frequently accessed and where denial-of-service attacks could disrupt critical business operations. According to CWE classification, this represents a CWE-415: Double Free vulnerability which falls under the broader category of memory safety issues that can lead to arbitrary code execution.
From an attack perspective, this vulnerability aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation and T1499: Endpoint Denial of Service as it could enable both system compromise through memory corruption and service disruption through kernel panics. The vulnerability affects systems running Linux kernels with SMB client implementations, particularly those that frequently interact with SMB servers or share files over network protocols. Network-based attackers who can influence the SMB connection state or trigger specific query operations may exploit this flaw to gain unauthorized access or cause system instability.
The recommended mitigation strategy involves applying the kernel patch that resets response bookkeeping structures before each attempt to prevent stale free operations. This fix ensures that response buffer tracking is properly maintained and prevents the accumulation of stale references that lead to double-free conditions. System administrators should prioritize updating their kernel versions to include this fix, particularly in environments where SMB services are actively used or where systems may be exposed to untrusted network traffic. Additionally, monitoring for unusual system behavior or kernel panics following SMB operations can help detect potential exploitation attempts before they cause significant damage to the system infrastructure.