Bug 2507081 (CVE-2026-64399)

Summary: CVE-2026-64399 kernel: ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: unspecified    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in ksmbd. This vulnerability allows a remote attacker to overwrite data on a shared file system due to insufficient permission checks in the FSCTL_DUPLICATE_EXTENTS_TO_FILE function. Even if a share is configured as read-only or a client has limited write attributes, an attacker can still modify the destination file's data, leading to unauthorized data alteration.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-07-25 10:03:59 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE

The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() overwrites the
destination file's data via vfs_clone_file_range() with neither the
share-level KSMBD_TREE_CONN_FLAG_WRITABLE check nor a per-handle
fp->daccess check that the other write-bearing arms carry. A client can
overwrite destination data on a read-only share, or from a handle opened
with only FILE_WRITE_ATTRIBUTES (which still yields an FMODE_WRITE filp).
FILE_WRITE_ATTRIBUTES-only destination handle overwrote the file's data via
the clone. Add both checks, matching the FSCTL_SET_SPARSE permission fix;
require FILE_WRITE_DATA since this writes data.
Comment 1 TEJ RATHI 2026-07-30 04:29:38 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072529-CVE-2026-64399-4ae6@gregkh/T