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VulnerabilityPublished Updated

CVE-2026-68100: Linux kernel · ksmbd: validate num_subauth when copying ACE in set_ntacl_dacl

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 8.1 High · fixed in fb3dc8e6da46a1ccad1956cda57de29d9b3033e0 : patch Linux kernel soon.

Data as of 26 Oct 2026, 17:30 UTC

CVSS 3.1 base score
8.1High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 37% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in fb3dc8e6da46a1ccad1956cda57de29d9b3033e0, e31fada5143784bc05c7ae44c79eed9b7a2e147e, b6d3cc6a524416dfdb2b47e4bba2e7e20011d056 +3
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < fb3dc8e6da46a1ccad1956cda57de29d9b3033e0
Fixed in
  • fb3dc8e6da46a1ccad1956cda57de29d9b3033e0
LinuxLinuxAffected
  • ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < e31fada5143784bc05c7ae44c79eed9b7a2e147e
Fixed in
  • e31fada5143784bc05c7ae44c79eed9b7a2e147e
LinuxLinuxAffected
  • ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < b6d3cc6a524416dfdb2b47e4bba2e7e20011d056
Fixed in
  • b6d3cc6a524416dfdb2b47e4bba2e7e20011d056
LinuxLinuxAffected
  • ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 47f0b34f6bc98ed85bfdc293e8f3e432ec24958d
Fixed in
  • 47f0b34f6bc98ed85bfdc293e8f3e432ec24958d
LinuxLinuxAffected
  • ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 26cb845e22a00c85bf566337417fa33492395f10
Fixed in
  • 26cb845e22a00c85bf566337417fa33492395f10
LinuxLinuxAffected
  • ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 5acbd3012fd4a7ccfebd91ea6f784120084eb897
Fixed in
  • 5acbd3012fd4a7ccfebd91ea6f784120084eb897

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().

References

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