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… (CVE-2026-64398)
Source GCVE Database
No CVSS score published yet
- Exploitation
Not in CISA KEV, no exploitation reported
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 39% of CVEs
What to do
AI-suggested
A fix has been implemented in the Linux kernel to add the missing permission check for FSCTL_SET_ZERO_DATA, requiring FILE_WRITE_DATA permission for this operation. Users should apply the official kernel update that includes this patch. Since no patch links or vendor advisories are provided here, check the Linux kernel mainline or distribution vendor advisories for the relevant fix. Patch status is not yet confirmed in this data—verify with vendor sources for current remediation guidance.
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.
References
- nvd.nist.gov/vuln/detail/CVE-2026-64398 (opens in a new tab)
- git.kernel.org/stable/c/25377f369688dd0bd814dc8965ed26d44238ecaa (opens in a new tab)
- git.kernel.org/stable/c/3072d82461f498c85daea8766e9d8bfbada31605 (opens in a new tab)
- git.kernel.org/stable/c/3320ba068198adc144c89d6661b805acce01735b (opens in a new tab)
- git.kernel.org/stable/c/57f2042fd87d7ce8fc3ac8b6c176e554df68b1a7 (opens in a new tab)
- git.kernel.org/stable/c/ca53bb17f4e8232cfaece3953d3cef62c559b039 (opens in a new tab)
- git.kernel.org/stable/c/deffa929086d7902e30918adf3dd27ccfe9c08b1 (opens in a new tab)