CVE-2026-64597 in Linux
Summary
by MITRE • 08/06/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix double-free in SMB2_close() replay
A response-bearing attempt can return a replayable error and free its response buffer. If SMB2_close_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 • 08/06/2026
This vulnerability exists within the Linux kernel's SMB client implementation where a double-free condition can occur during SMB2_close() operation handling. The flaw manifests when the SMB2_close_init() function fails prior to sending a subsequent request, causing the system to attempt freeing memory that has already been released. This represents a classic memory corruption vulnerability that can lead to system instability and potential exploitation by malicious actors.
The technical root cause stems from improper response buffer management within the SMB protocol implementation. When an error condition occurs during the initialization phase of SMB2_close operations, the system maintains references to previously allocated response buffers while simultaneously attempting to free them again. This creates a scenario where the same memory address gets deallocated twice, resulting in undefined behavior that can manifest as kernel panics, system crashes, or memory corruption. The vulnerability specifically impacts the client-side SMB implementation and operates at the kernel level where such memory management errors can have severe consequences.
The operational impact of this double-free vulnerability extends beyond simple system instability to potentially enable privilege escalation or denial of service conditions. Attackers could exploit this flaw by crafting specific SMB responses that trigger the problematic code path, leading to system crashes or in worst-case scenarios, arbitrary code execution within kernel space. The vulnerability is particularly concerning because it occurs during routine file close operations, making it difficult to detect and potentially exploitable in automated attacks against systems running affected kernel versions.
Mitigation strategies should focus on implementing proper response buffer bookkeeping reset procedures before each send attempt as recommended in the patch. System administrators should prioritize applying kernel updates that contain the fix for this vulnerability, particularly in environments where SMB services are actively used. Additional defensive measures include monitoring for unusual system crashes or memory allocation patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-415 which addresses double free conditions in memory management, and could be categorized under ATT&CK technique T1059 for command and scripting interpreter usage in exploitation scenarios. Organizations should also consider implementing network segmentation and access controls to limit SMB service exposure and reduce attack surface while awaiting patch deployment.
The fix implemented addresses the core issue by ensuring that response bookkeeping information is properly reset before each attempt, preventing stale references from causing duplicate free operations. This approach aligns with secure coding practices that emphasize proper resource management and memory lifecycle handling in kernel space operations. Regular security assessments of SMB implementations should include verification of proper error handling and cleanup procedures to prevent similar vulnerabilities from emerging in other protocol components or subsystems.