CVE-2026-68098 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: bound DACL dedup walk to copied ACEs
set_ntacl_dacl() can stop copying ACEs before consuming the full input DACL when size accounting overflows.
When that happens, num_aces reflects only the ACEs that were actually copied into the output DACL, but set_posix_acl_entries_dacl() still receives nt_num_aces and uses it to walk the existing ACE array during dedup.
That makes the dedup walk scan past the copied ACE array and inspect buffer tail that does not contain valid ACEs.
Split the two meanings currently carried by the NT ACE count. Pass the number of copied NT ACEs to bound the dedup walk, and preserve the original "input DACL had NT ACEs" state separately for the Everyone/default ACL fallback.
This keeps the dedup walk aligned with the ACEs that are actually present in the rebuilt DACL.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability resides within the Linux kernel's ksmbd implementation, specifically in how it handles discretionary access control lists for SMB file sharing operations. This issue manifests as a buffer overread condition that occurs during the processing of NT ACL (Access Control List) structures when the system attempts to deduplicate Access Control Entries. The flaw stems from improper handling of size accounting during the copying process of ACEs, creating a scenario where the internal state becomes inconsistent between the actual copied data and the operational logic that processes this data.
The technical root cause involves the set_ntacl_dacl() function which manages the copying of Access Control Entries from an input DACL to an output DACL structure. When integer overflow occurs during size calculations, the function terminates early, leaving some ACEs unprocessed in the input stream while still updating the accounting variables. This creates a discrepancy where num_aces correctly reflects only the copied ACE count but nt_num_aces retains the original input value for downstream processing. The set_posix_acl_entries_dacl() function then uses this corrupted nt_num_aces value to traverse what it believes is the complete ACE array, but instead accesses memory beyond the bounds of the actually copied data.
This buffer overread condition creates significant operational risks including potential information disclosure through memory corruption, system stability degradation, and possible privilege escalation vectors. The vulnerability operates at the kernel level within the SMB file sharing subsystem, making it particularly dangerous as it could be exploited by remote attackers to gain unauthorized access to shared resources or compromise the integrity of the entire system. The flaw specifically targets the deduplication mechanism that should prevent duplicate ACE entries but instead causes memory corruption during this process.
The security implications align with CWE-129, which addresses improper validation of array indices, and CWE-787, concerning out-of-bounds writes. From an ATT&CK perspective, this vulnerability could enable initial access through network services and potentially lead to privilege escalation or lateral movement within compromised systems. The fix implemented separates the dual meanings previously carried by the NT ACE count variable, ensuring that the deduplication walk operates only on the actual copied ACEs rather than on a corrupted accounting value. This approach maintains proper bounds checking and prevents the traversal of invalid memory regions while preserving the correct fallback behavior for default ACL handling.
The mitigation strategy focuses on maintaining separate accounting variables for the actual copied ACE count versus the original input state, ensuring that the deduplication process operates within properly bounded memory regions. This solution addresses the fundamental issue of state inconsistency while preserving all legitimate functionality of the SMB file sharing implementation. The fix prevents potential exploitation by ensuring that buffer operations remain within safe boundaries and eliminates the possibility of accessing uninitialized or corrupted memory regions during ACL processing operations.