CVE-2026-68100
Received Received - Intake

Heap Out-of-Bounds Read in ksmbd set_ntacl_dacl

Publication date: 2026-08-10

Last updated on: 2026-08-10

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate num_subauth when copying ACE in set_ntacl_dacl set_ntacl_dacl() copies each ACE from the attacker-controlled stored security descriptor verbatim into the response DACL without checking sid.num_subauth. The ACE bytes (including an unchecked num_subauth) originate from an authenticated SMB2_SET_INFO(SecInfo=DACL) that is stored raw via ksmbd_vfs_set_sd_xattr(); parse_dacl() rejects a bad ACE with `break` rather than an error, so parse_sec_desc() still returns success and the malformed SD reaches the xattr intact. On a subsequent SMB2_QUERY_INFO(SecInfo=DACL) for an inode carrying a POSIX access ACL, build_sec_desc() -> set_ntacl_dacl() -> set_posix_acl_entries_dacl() walks the copied ACEs and reads ntace->sid.sub_auth[ntace->sid.num_subauth - 1] with num_subauth taken straight from the stored SD. Since sub_auth[] is fixed at SID_MAX_SUB_AUTHORITIES (15), a crafted num_subauth (e.g. 255) drives an out-of-bounds heap read of ~1 KB with an offset fully controlled by an authenticated client. The sibling functions already gate this field: parse_dacl() -- num_subauth == 0 || > SID_MAX_SUB_AUTHORITIES parse_sid() -- num_subauth > SID_MAX_SUB_AUTHORITIES smb_copy_sid() -- min_t(u8, num_subauth, SID_MAX_SUB_AUTHORITIES) set_ntacl_dacl() is the lone inconsistent path that omits the check. Add the same num_subauth validation in set_ntacl_dacl() before copying the ACE, matching the gate already enforced by parse_dacl().

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Meta Information

Published
2026-08-10
Last Modified
2026-08-10
Generated
2026-08-10
AI Q&A
2026-08-10
EPSS Evaluated
N/A
NVD
CVE-2026-68100
EUVD
EUVD-2026-55481

Affected Vendors & Products

Currently, no data is known.

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves improper validation of the num_subauth field when copying Access Control Entries (ACEs) in the set_ntacl_dacl function. An attacker can exploit this to trigger an out-of-bounds heap read by crafting a malformed security descriptor with an excessive num_subauth value. The issue arises because set_ntacl_dacl does not validate num_subauth, unlike other functions in the codebase.

Detection Guidance

This vulnerability involves a heap out-of-bounds read in the Linux kernel's ksmbd module due to improper validation of num_subauth in SMB ACEs. Detection requires checking kernel logs for crashes or memory corruption events related to ksmbd. Monitor for SMB2_SET_INFO or SMB2_QUERY_INFO requests with malformed DACLs. Use kernel oops logs or tools like dmesg to identify heap corruption or invalid memory access patterns.

Impact Analysis

An authenticated attacker could exploit this flaw to read sensitive kernel memory, potentially leading to information disclosure or system instability. The vulnerability requires an attacker to have valid SMB credentials to send crafted requests, limiting the attack surface to authenticated users.

Mitigation Strategies

Apply the latest Linux kernel security patches that include the fix for CVE-2026-68100. Disable the ksmbd module if not in use by unloading the module with rmmod ksmbd. Restrict SMB access via firewall rules to trusted networks only. Monitor for unusual SMB traffic patterns that may indicate exploitation attempts.

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