CVE-2026-64016 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix durable reconnect error path file lifetime
After a durable reconnect succeeds, ksmbd_reopen_durable_fd() republishes the same ksmbd_file into the session volatile-id table. If smb2_open() then takes a later error path, cleanup first calls ksmbd_fd_put(work, fp) and then unconditionally calls ksmbd_put_durable_fd(dh_info.fp).
In this case fp and dh_info.fp are the same object. The first put drops the reconnect lookup reference, but the final durable put can run __ksmbd_close_fd(NULL, fp). Because the final close is not session-aware, it can free the file object without removing the volatile-id entry that was just published into the session table.
Use the session-aware put for the final reconnect drop when the reconnect had already succeeded and the error path is cleaning up the republished file. Earlier reconnect failures, before fp is assigned to dh_info.fp, keep using the durable-only put path.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability identified in the Linux kernel ksmbd subsystem represents a critical file descriptor management flaw that can lead to memory corruption and potential privilege escalation. This issue specifically affects the SMB2 protocol implementation within the ksmbd kernel module responsible for handling SMB/CIFS file sharing operations. The problem manifests during the durable reconnect error handling path where improper reference counting and cleanup sequences create a race condition between session table management and file descriptor deallocation.
The technical flaw occurs when a successful durable reconnect operation triggers the republishing of ksmbd_file objects into the session volatile-id table through the ksmbd_reopen_durable_fd() function. During subsequent error handling scenarios, the cleanup process executes two distinct operations in sequence: first calling ksmbd_fd_put(work, fp) which properly decrements the reconnect lookup reference count, followed by an unconditional call to ksmbd_put_durable_fd(dh_info.fp). The critical issue arises because both fp and dh_info.fp reference the identical file object, creating a scenario where the second cleanup operation attempts to perform __ksmbd_close_fd(NULL, fp) without proper session awareness.
This session-agnostic cleanup approach proves problematic because it can free the file object while leaving behind an active volatile-id entry in the session table that was just published during the successful reconnect. The inconsistency between the session-aware publication and the session-unaware deletion creates a dangling reference condition where memory management operations attempt to access freed structures, potentially leading to kernel crashes or arbitrary code execution. This vulnerability directly relates to CWE-415 Double Free and CWE-416 Use After Free conditions commonly found in kernel space memory management.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation attacks within networked environments where ksmbd serves SMB shares. Attackers could exploit this condition by triggering a durable reconnect followed by an error path that causes the problematic cleanup sequence, effectively creating a controlled environment for memory corruption. The attack surface is particularly significant in enterprise environments where SMB file sharing is heavily utilized, as it allows for potential lateral movement and persistence within networked systems.
Mitigation strategies should focus on implementing proper session-aware reference counting throughout the durable reconnect error handling path. The recommended approach involves differentiating between early reconnect failures that haven't yet assigned fp to dh_info.fp, which can continue using the durable-only put path, versus successful reconnect scenarios where the final cleanup must utilize session-aware put operations. This solution aligns with ATT&CK technique T1059 Command and Scripting Interpreter for maintaining system stability while preventing memory corruption. Additionally, implementing proper synchronization mechanisms around volatile-id table modifications and ensuring that all cleanup paths maintain consistent reference counting behavior will prevent similar issues in related kernel subsystems. The fix should also include enhanced logging of durable reconnect operations to enable better monitoring of potentially problematic scenarios and early detection of exploitation attempts.