CVE-2026-98450 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: close completed creates on compound wait errors
compound_send_recv() waits for responses in order. If a later wait is interrupted, or if a later MID fails during response synchronization, an earlier CREATE may already have opened a remote handle. The earlier mid is then released without invoking handle_cancelled_mid(), leaving the remote handle open because no FID was copied to the caller.
Mark completed earlier mids as cancelled when a compound wait or MID synchronization aborts. Keep their response buffers attached while the MIDs are synchronized, and transfer them only after synchronization of the processed responses, so the release path can inspect successful CREATE responses and queue SMB2_close() after a later failure. Account for a remote open only after the close work is allocated and before it is queued, since the caller has not yet updated num_remote_opens. Mark the create+close compound used by smb2_unlink() so it is not closed again. Non-CREATE responses and compounds that already include a close keep their existing behavior.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel SMB client implementation contains a logic flaw in the handling of compound server message block requests, specifically within the compound_send_recv function which orchestrates the sending and receiving of multiple protocol operations as a single atomic unit. This vulnerability arises from an incorrect synchronization mechanism when processing responses for these compound transactions. Under normal operation, the client sends a sequence of related commands, such as creating a file handle followed by closing it or performing other metadata updates, expecting all parts to succeed together. However, if a later wait in this chain is interrupted by a signal or if a subsequent Message Identifier fails during response synchronization, an earlier CREATE command may have already successfully opened a remote file handle on the server side. The critical technical flaw lies in how these early successes are handled when the overall compound operation ultimately aborts due to the failure of a later component. Instead of properly cleaning up the resources associated with the successful intermediate steps, the code releases the corresponding MID without invoking the necessary handle_cancelled_mid routine. This oversight results in the remote file handle remaining open on the server because no File ID was copied back to the caller application, leaving an orphaned resource that consumes server-side memory and potentially locks files unexpectedly for other users or processes.
This issue represents a classic case of improper cleanup during error handling paths within network protocol implementations, aligning with CWE-401 which describes missing release of resources after successful allocation. The operational impact is significant as it leads to resource leaks on the SMB server, which can degrade performance over time and potentially lead to denial of service conditions if an attacker or misbehaving client repeatedly triggers these compound failures while leaving handles open. Furthermore, because the caller is not informed that a handle was opened but subsequently abandoned without proper closure semantics, applications may experience unexpected behavior when attempting to access those files later, such as encountering permission denied errors due to existing locks held by the orphaned session. The vulnerability also touches upon CWE-362 regarding concurrent execution issues where race conditions or improper synchronization lead to inconsistent state management between the client and server.
The resolution involves a comprehensive restructuring of how compound responses are processed and released. The fix ensures that when a compound wait is aborted or MID synchronization fails, all earlier completed MIDs within that same transaction block are explicitly marked as cancelled rather than simply being discarded. To facilitate this proper cleanup, the implementation keeps response buffers attached to their respective MIDs during the entire synchronization phase instead of detaching them prematurely. These buffers are only transferred after the successful synchronization of processed responses is complete. This allows the release path to inspect any successful CREATE responses and automatically queue an SMB2_close command for those handles before the transaction context is fully torn down. Additionally, the fix accounts for remote opens by ensuring they are tracked correctly relative to when close work is allocated but not yet queued, preventing double-closing scenarios particularly in operations like smb2_unlink which inherently use a create-and-close compound pattern. Non-CREATE responses and compounds that already include explicit close instructions retain their existing behavior to maintain backward compatibility and stability for unaffected code paths.
From a defensive perspective, this patch highlights the importance of rigorous state management in network protocol clients where partial successes must be rolled back atomically. System administrators should ensure that Linux kernels are updated with patches addressing this SMB client logic error to prevent potential resource exhaustion on file servers interacting with vulnerable clients. For developers maintaining kernel modules or custom SMB implementations, it serves as a reminder to always verify cleanup paths for all intermediate steps in compound operations, ensuring that any side effects like opened handles are neutralized if the overall transaction fails. This aligns with ATT&CK techniques related to resource manipulation and can help mitigate risks associated with local privilege escalation attempts that might leverage such resource leaks to destabilize system services or interfere with other users' access to shared resources.