CVE-2026-64398
Received Received - Intake

BaseFortify

Publication date: 2026-07-25

Last updated on: 2026-07-25

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ksmbd: add a permission check for FSCTL_SET_ZERO_DATA FSCTL_SET_ZERO_DATA in smb2_ioctl() destroys file data via ksmbd_vfs_zero_data() -> vfs_fallocate(PUNCH_HOLE/ZERO_RANGE) after checking only the share-level KSMBD_TREE_CONN_FLAG_WRITABLE, with no per-handle access check. A handle opened with only FILE_WRITE_ATTRIBUTES still yields an FMODE_WRITE filp (FILE_WRITE_ATTRIBUTES is part of FILE_WRITE_DESIRE_ACCESS_LE, so smb2_create_open_flags() opens it O_WRONLY), so the vfs_fallocate FMODE_WRITE check does not stop it; only the missing fp->daccess gate would. Reproduced on mainline 7.1-rc7 with KASAN by an authenticated SMB client: a FILE_WRITE_ATTRIBUTES-only handle zeroed 4096 bytes of file data it had no FILE_WRITE_DATA right to (6/6; a FILE_READ_DATA-only handle was correctly denied). This is the unfixed sibling of commit cc57232cae23 ("ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE"). Because SET_ZERO_DATA writes data (not an attribute), require FILE_WRITE_DATA.

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Meta Information

Published
2026-07-25
Last Modified
2026-07-25
Generated
2026-07-25
AI Q&A
2026-07-25
EPSS Evaluated
N/A
NVD
CVE-2026-64398
EUVD
EUVD-2026-48942

Affected Vendors & Products

Currently, no data is known.

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a permission bypass in the ksmbd module. The issue occurs when handling the FSCTL_SET_ZERO_DATA control code, which is used to zero out file data. The vulnerability allows an authenticated SMB client to zero file data even when they only have FILE_WRITE_ATTRIBUTES permissions, bypassing proper access checks. This happens because the code only checks share-level writability and not per-handle access rights.

Impact Analysis

If exploited, this vulnerability could allow an attacker with limited permissions to overwrite or destroy file data they should not have access to. This could lead to data loss, corruption, or unauthorized modifications. The attack requires an authenticated SMB client connection, so it primarily affects systems using ksmbd for SMB file sharing.

Compliance Impact

This vulnerability could impact compliance by enabling unauthorized data modification or destruction, violating integrity requirements in GDPR and HIPAA. GDPR mandates data integrity and protection, while HIPAA requires safeguards for protected health information. Exploitation could lead to unauthorized changes, breaching these compliance standards.

Mitigation Strategies

Update the Linux kernel to a patched version that includes the fix for this vulnerability. The issue is resolved by ensuring proper permission checks for FSCTL_SET_ZERO_DATA operations in the ksmbd module.

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