CVE-2026-64394VulnerabilityPublished 07/25/2026

In the Linux kernel, the following vulnerability has been resolved: ksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2…

Source GCVE Database

ghsa-hj5q-pp4q-jpfg

Not known to be exploited.

Data as of 10/24/2026, 22:16:04 UTC

Severity

High

No CVSS score from NVD or the CNA

Exploitation: Not in CISA KEV, no exploitation reported
EPSS: 0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

What to do

AI-suggested

Until an official fix is available, restrict access to SMB2 shares and monitor for unusual permission changes. Once a patch is released, apply it promptly to ensure the WRITE_DAC/WRITE_OWNER permission checks are enforced on SMB2 SET_INFO SECURITY operations.

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY commit cc57232cae23 ("ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE") added a fp->daccess gate to fsctl_set_sparse and noted that "similar handle-level checks exist in other functions but are missing here." The SMB2 SET_INFO SECURITY arm is one of the missing ones, and the most security-relevant: smb2_set_info_sec() calls set_info_sec() with no per-handle access check. set_info_sec() (fs/smb/server/smbacl.c) re-permissions the file: it rewrites owner/group/mode via notify_change(), rewrites the POSIX ACL via set_posix_acl(), and on KSMBD_SHARE_FLAG_ACL_XATTR shares removes and rewrites the Windows security descriptor via ksmbd_vfs_set_sd_xattr(). Every other persistent-mutation arm of the sibling handler smb2_set_info_file() checks fp->daccess first (FILE_WRITE_DATA / FILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm — which mutates the access control itself — is the only one with no gate. A client can therefore open a handle with FILE_WRITE_ATTRIBUTES only (no FILE_WRITE_DAC / FILE_WRITE_OWNER) and use SMB2_SET_INFO with InfoType SMB2_O_INFO_SECURITY to rewrite the file's DACL and owner, granting itself access the handle's daccess never carried. Unlike the FSCTL data arms this is a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop — the missing fp->daccess check is the entire gate. Setting a security descriptor is the WRITE_DAC / WRITE_OWNER operation, so require at least one of those on the handle before re-permissioning the file. -EACCES is mapped to STATUS_ACCESS_DENIED by smb2_set_info().

Impact

An attacker with a handle possessing only FILE_WRITE_ATTRIBUTES permission could exploit this vulnerability to modify file ownership and access control lists, thereby escalating their privileges on the affected file. This could lead to unauthorized access or control over files by bypassing intended permission restrictions. The vulnerability affects the integrity and access control enforcement of the SMB2 server implementation in the Linux kernel.

Summary

The Linux kernel's ksmbd SMB2 server had a security flaw where the SMB2 SET_INFO SECURITY operation did not enforce the necessary WRITE_DAC or WRITE_OWNER permission checks on file handles. While other SMB2 SET_INFO operations verify handle-level access rights before modifying file metadata, the SECURITY arm called set_info_sec() without verifying if the handle had the appropriate permissions. This allowed a client holding only FILE_WRITE_ATTRIBUTES permission to rewrite the file's discretionary access control list (DACL) and owner, effectively escalating privileges on the file. The vulnerability was fixed by adding the required WRITE_DAC/WRITE_OWNER checks to the SMB2 SET_INFO SECURITY code path, ensuring that only authorized handles can modify security descriptors.

References

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