PT-2026-64615 · Linux · Linux
CVE-2026-64394
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Publicado
2026-07-25
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Atualizado
2026-07-25
Nenhuma
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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().
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