EUVD-2026-30503
GHSA-9hm7-v4rj-6wqj
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
4DescriptionNVD
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate inherited ACE SID length
smb_inherit_dacl() walks the parent directory DACL loaded from the security descriptor xattr. It verifies that each ACE contains the fixed SID header before using it, but does not verify that the variable-length SID described by sid.num_subauth is fully contained in the ACE.
A malformed inheritable ACE can advertise more subauthorities than are present in the ACE. compare_sids() may then read past the ACE. smb_set_ace() also clamps the copied destination SID, but used the unchecked source SID count to compute the inherited ACE size. That could advance the temporary inherited ACE buffer pointer and nt_size accounting past the allocated buffer.
Fix this by validating the parent ACE SID count and SID length before using the SID during inheritance. Compute the inherited ACE size from the copied SID so the size matches the bounded destination SID. Reject the inherited DACL if size accumulation would overflow smb_acl.size or the security descriptor allocation size.
AnalysisAI
Out-of-bounds read and buffer overflow in the Linux kernel's ksmbd SMB server allows authenticated remote attackers to corrupt memory or read past allocated buffers by sending a malformed inheritable ACE with an inflated num_subauth value. The flaw resides in smb_inherit_dacl() and smb_set_ace(), where the variable-length SID is not bounds-checked during DACL inheritance, enabling heap corruption with potential for remote code execution against any SMB server using ksmbd. …
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RemediationAI
Within 24 hours: Identify all systems running Linux kernel with ksmbd SMB server and their current kernel versions. Within 7 days: Apply vendor-released patches to affected systems across all stable branches per Linux distribution guidance (Red Hat, Canonical, Ubuntu, etc.). …
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