CVE-2026-68100
HighCVSS 8.1Exploitation Probability (EPSS)
Low risk34th percentile - higher than 34% of all known CVEs
Summary
In the Linux kernel, the ksmbd (SMB server) module has a vulnerability due to missing validation of the num_subauth field when copying ACE entries in the set_ntacl_dacl function. A malicious authenticated client can send a crafted security descriptor with an invalid num_subauth value, leading to an out-of-bounds heap read of approximately 1 KB.
Risk Assessment
The vulnerability allows an authenticated SMB client to read kernel memory, potentially leading to disclosure of sensitive information or system instability. The attack requires access to the ksmbd service but does not require administrative privileges.
Recommendation
It is recommended to immediately apply the Linux kernel patch that adds num_subauth validation in set_ntacl_dacl. If the kernel cannot be updated, restrict access to the ksmbd service to trusted clients only.
Original NVD description (English source)
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().