CVE-2026-52996
Received Received - Intake
BaseFortify

Publication date: 2026-06-24

Last updated on: 2026-06-24

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix durable fd leak on ClientGUID mismatch in durable v2 open ksmbd_lookup_fd_cguid() returns a ksmbd_file with its refcount incremented via ksmbd_fp_get(). parse_durable_handle_context() in the DURABLE_REQ_V2 case properly releases this reference on every path inside the ClientGUID-match branch, either by calling ksmbd_put_durable_fd() or by transferring ownership to dh_info->fp for a successful reconnect. However, when an entry exists in the global file table with the same CreateGuid but a different ClientGUID, the code simply falls through to the new-open path without dropping the reference obtained from ksmbd_lookup_fd_cguid(). Per MS-SMB2 section 3.3.5.9.10 ("Handling the SMB2_CREATE_DURABLE_HANDLE_REQUEST_V2 Create Context"), the server MUST locate an Open whose Open.CreateGuid matches the request's CreateGuid AND whose Open.ClientGuid matches the ClientGuid of the connection that received the request. If no such Open is found, the server MUST continue with the normal open execution phase. A CreateGuid hit with a ClientGUID mismatch is therefore the "Open not found" case: proceeding with a new open is correct, but the reference obtained purely as a side effect of the lookup must not be leaked. Repeated requests that hit this mismatch pin global_ft entries, prevent __ksmbd_close_fd() from ever running for the corresponding files, and defeat the durable scavenger, leading to long-lived resource leaks. Release the reference in the mismatch path and clear dh_info->fp so subsequent logic does not mistake a non-matching lookup result for a reconnect target.
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Meta Information
Published
2026-06-24
Last Modified
2026-06-24
Generated
2026-06-25
AI Q&A
2026-06-24
EPSS Evaluated
N/A
NVD
CVE-2026-52996
EUVD
EUVD-2026-38864
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux_kernel ksmbd *
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's ksmbd component, specifically related to handling durable file descriptors (fd) during SMB2 durable handle requests (version 2). When a ClientGUID mismatch occurs during a lookup of a file descriptor by its CreateGuid, the code fails to properly release a reference count on the file descriptor. This happens because the code proceeds with a new open operation without dropping the reference obtained from the lookup, leading to a resource leak.

According to the MS-SMB2 protocol, the server must find an open file whose CreateGuid and ClientGuid both match the request. If the ClientGuid does not match, the server should treat it as an "Open not found" case and proceed with a new open. However, the existing code leaks the reference count in this mismatch scenario, causing pinned entries in the global file table and preventing proper cleanup.

Mitigation Strategies

The vulnerability is fixed in the Linux kernel by ensuring that the reference obtained from ksmbd_lookup_fd_cguid() is properly released when there is a ClientGUID mismatch in durable v2 open requests.

To mitigate this vulnerability immediately, you should update your Linux kernel to a version that includes this fix.

Impact Analysis

This vulnerability can lead to long-lived resource leaks in the Linux kernel's ksmbd service. Specifically, repeated requests that trigger the ClientGUID mismatch cause file descriptor references to be pinned indefinitely, preventing the normal closing and cleanup of these resources.

As a result, system resources such as file descriptors and memory may be exhausted over time, potentially degrading system performance or causing denial of service conditions due to resource exhaustion.

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