CVE-2026-64383 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix double-free in SMB2_flush() replay
SMB2_flush() keeps its response buffer bookkeeping across replay attempts. If a replayable flush response is received and the retry then fails before cifs_send_recv() stores a replacement response, flush_exit will free the stale response pointer a second time.
Reinitialize resp_buftype and rsp_iov at the top of the replay loop so cleanup only acts on response state produced by the current attempt. This fixes a double-free without changing replay handling for successful requests.
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Analysis
by VulDB Data Team • 07/26/2026
The vulnerability resides in the Linux kernel's SMB client implementation, specifically within the smb2_flush() function that handles flush operations for SMB2 protocol connections. This flaw represents a classic double-free error that occurs during the replay mechanism of SMB operations, where the system attempts to recover from failed network transactions by retrying them. The issue manifests when the SMB client encounters a scenario where a flush request must be replayed due to transient network failures or other temporary issues during communication with SMB servers.
The technical root cause stems from improper response buffer management within the replay loop of the smb2_flush() function. When a replayable flush response is received and subsequent retry attempts fail before the cifs_send_recv() function successfully stores a replacement response, the cleanup code executes and frees the stale response pointer. However, due to the flawed bookkeeping mechanism, this same pointer gets freed a second time during the normal exit path of flush_exit function, leading to memory corruption that could potentially be exploited by malicious actors.
This vulnerability operates at the kernel level and affects systems running Linux kernels with SMB client functionality enabled, particularly those connecting to SMB2/SMB3 servers. The double-free condition creates an opportunity for memory corruption that could allow attackers to manipulate heap structures, potentially leading to privilege escalation or system instability. The flaw is particularly concerning because it occurs during normal network operation when the system attempts to recover from transient failures, making it difficult to predict and prevent.
The fix implemented addresses the core issue by reinitializing the resp_buftype and rsp_iov variables at the beginning of each replay loop iteration. This ensures that cleanup operations only reference response state that was actually generated during the current attempt rather than carrying over stale references from previous failed attempts. The solution maintains the existing replay handling logic for successful requests while preventing the double-free condition through proper initialization of response tracking variables before each retry cycle.
This vulnerability aligns with CWE-415, which describes double free conditions in software systems, and represents a memory safety issue that could potentially map to ATT&CK technique T1059.007 for command and scripting interpreter usage if exploited through compromised system processes. The fix demonstrates proper defensive programming practices by ensuring clean state management during error recovery scenarios. The resolution maintains backward compatibility while strengthening the SMB client's resilience against transient network failures without altering the fundamental behavior of successful request processing, making it a targeted and minimal change that reduces attack surface while preserving functionality.