CVE-2026-68097 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate ACE size against SID sub-authorities
set_ntacl_dacl() validates sid.num_subauth before copying an ACE, but does not verify that the declared ACE size contains all sub-authorities described by that field. An undersized ACE can therefore be copied and later make the POSIX ACL deduplication walk inspect data beyond the copied ACE boundary.
The existing initial bound check is also too small. It only ensures that the ACE size field is accessible before set_ntacl_dacl() reads sid.num_subauth farther into the input buffer.
Require enough input for the fixed SID header before accessing num_subauth, reject ACEs smaller than that header, and skip ACEs whose declared size cannot contain the complete SID. This makes the validation consistent with the other ACE walk paths.
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Analysis
by VulDB Data Team • 08/11/2026
The vulnerability identified in the Linux kernel ksmbd subsystem represents a critical buffer overflow condition that arises from inadequate validation of Access Control Entry (ACE) structures during NT ACL processing. This flaw specifically affects the set_ntacl_dacl() function which handles the conversion of Windows-style ACLs to POSIX ACLs for SMB file sharing operations. The issue stems from insufficient bounds checking when processing Security Identifier (SID) sub-authorities within ACE structures, creating a potential pathway for malicious data manipulation that could lead to arbitrary code execution or system compromise.
The technical flaw manifests in the improper validation sequence where the function first reads the sid.num_subauth field without ensuring adequate input buffer space for the complete SID structure. This initial bound check is fundamentally flawed because it only verifies that the ACE size field itself is accessible rather than confirming that the entire ACE contains sufficient space to accommodate all sub-authorities referenced by the num_subauth field. When an undersized ACE is processed, the system copies incomplete data structures that later cause the POSIX ACL deduplication routine to access memory beyond the intended buffer boundaries, resulting in information disclosure or potential code execution.
The operational impact of this vulnerability extends across multiple security domains within the Linux SMB implementation, particularly affecting systems running ksmbd services that handle Windows-style file permissions. Attackers could exploit this weakness by crafting malicious NT ACL structures with deliberately truncated ACE entries, potentially leading to privilege escalation, denial of service conditions, or unauthorized data access. The vulnerability is especially concerning in enterprise environments where SMB file sharing is extensively used, as it could be leveraged to compromise file server security and access control mechanisms.
This issue aligns with CWE-129, which addresses improper validation of input boundaries, and demonstrates characteristics consistent with ATT&CK technique T1068, involving local privilege escalation through kernel vulnerabilities. The vulnerability also reflects broader concerns in the SMB protocol implementation where inadequate input sanitization creates multiple attack vectors for memory corruption exploits. The fix implemented requires enforcing proper input validation by ensuring sufficient buffer space exists for complete SID headers before accessing sub-authority fields, rejecting ACEs that are smaller than minimum header requirements, and skipping entries whose declared size cannot accommodate the referenced SID structure.
The mitigation strategy involves implementing comprehensive validation checks that align with standard security practices for buffer management and input sanitization. This includes requiring adequate input space for fixed SID headers before processing num_subauth fields, establishing minimum ACE size requirements that account for complete SID structures, and ensuring all ACE walk paths maintain consistent validation approaches. The solution addresses the root cause by making the validation logic consistent across different code paths within the SMB implementation, thereby preventing similar issues in related functions that process ACE structures. This approach follows industry best practices for kernel security and aligns with secure coding guidelines that emphasize defensive programming and input validation as primary defense mechanisms against buffer overflow vulnerabilities.
The fix also demonstrates proper adherence to security standards including those outlined in the Common Weakness Enumeration framework and ATT&CK matrix, specifically addressing weaknesses in input validation and buffer management. By ensuring that all ACE processing functions maintain consistent boundary checking behavior, the solution reduces the attack surface for similar vulnerabilities in related kernel subsystems. The implementation reinforces the principle of least privilege and secure by design approaches in kernel development, where proper input validation serves as the first line of defense against memory corruption exploits. This vulnerability resolution contributes to overall system security by preventing potential escalation paths that could be exploited by malicious actors targeting SMB services in Linux environments.