CVE-2026-43490 (GCVE-0-2026-43490)

Vulnerability from cvelistv5 – Published: 2026-05-15 05:15 – Updated: 2026-08-05 12:28
VLAI
Title
ksmbd: validate inherited ACE SID length
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate inherited ACE SID length smb_inherit_dacl() walks the parent directory DACL loaded from the security descriptor xattr. It verifies that each ACE contains the fixed SID header before using it, but does not verify that the variable-length SID described by sid.num_subauth is fully contained in the ACE. A malformed inheritable ACE can advertise more subauthorities than are present in the ACE. compare_sids() may then read past the ACE. smb_set_ace() also clamps the copied destination SID, but used the unchecked source SID count to compute the inherited ACE size. That could advance the temporary inherited ACE buffer pointer and nt_size accounting past the allocated buffer. Fix this by validating the parent ACE SID count and SID length before using the SID during inheritance. Compute the inherited ACE size from the copied SID so the size matches the bounded destination SID. Reject the inherited DACL if size accumulation would overflow smb_acl.size or the security descriptor allocation size.
Severity
8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < a7fb771314fb3a265d30f8ac245869a367ab065c (git)
Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < 47c6e37a77b10e74f70d845ba4ea5d3cafa00336 (git)
Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < 1aa60fea7f637c071f529ad6784aecca2f2f0c5f (git)
Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < c1d95c995d5bcb24b639200a899eda59cb1e6d64 (git)
Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < 996454bc0da84d5a1dedb1a7861823087e01a7ae (git)
Create a notification for this product.
Linux Linux Affected: 5.15
Unaffected: 0 , < 5.15 (semver)
Unaffected: 6.6.141 , ≤ 6.6.* (semver)
Unaffected: 6.12.88 , ≤ 6.12.* (semver)
Unaffected: 6.18.30 , ≤ 6.18.* (semver)
Unaffected: 7.0.7 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate inherited ACE SID length\n\nsmb_inherit_dacl() walks the parent directory DACL loaded from the\nsecurity descriptor xattr. It verifies that each ACE contains the fixed\nSID header before using it, but does not verify that the variable-length\nSID described by sid.num_subauth is fully contained in the ACE.\n\nA malformed inheritable ACE can advertise more subauthorities than are\npresent in the ACE. compare_sids() may then read past the ACE.\nsmb_set_ace() also clamps the copied destination SID, but used the\nunchecked source SID count to compute the inherited ACE size. That could\nadvance the temporary inherited ACE buffer pointer and nt_size accounting\npast the allocated buffer.\n\nFix this by validating the parent ACE SID count and SID length before\nusing the SID during inheritance. Compute the inherited ACE size from the\ncopied SID so the size matches the bounded destination SID. Reject the\ninherited DACL if size accumulation would overflow smb_acl.size or the\nsecurity descriptor allocation size."
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              "value": "AV:N - The vulnerable code is in ksmbd SMB server ACL inheritance, reached through SMB2 requests over the network.\nAC:L - An attacker who can write to an ACL-xattr-enabled share can deterministically plant a malformed parent DACL and create a child to trigger inheritance.\nPR:L - The path is post-authentication and requires a valid SMB session/tree connection with write/create ability on the share.\nUI:N - No victim action is needed after the attacker has SMB access; the attacker sends the SET_INFO/CREATE requests directly.\nS:U - The corruption occurs inside the kernel serving the SMB share and does not cross a separate security authority boundary.\nC:H - The bug includes out-of-bounds reads from kernel heap data, and the inherited security descriptor can expose copied data or support stronger exploitation.\nI:H - The unchecked SID length can advance the inherited ACE buffer pointer past its allocation, enabling kernel heap out-of-bounds writes with attacker-influenced ACE data.\nA:H - The same heap corruption and out-of-bounds access can crash or panic the kernel, causing high availability impact."
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That could\\nadvance the temporary inherited ACE buffer pointer and nt_size accounting\\npast the allocated buffer.\\n\\nFix this by validating the parent ACE SID count and SID length before\\nusing the SID during inheritance. Compute the inherited ACE size from the\\ncopied SID so the size matches the bounded destination SID. 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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-06-28T07:38:10+00:00",
      "cve": "CVE-2026-43490",
      "id": "CVE-2026-43490",
      "initial_release_date": "2026-05-15T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: validate inherited ACE SID length",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-43490.json",
      "version": "3"
    },
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      "current_release_date": "2026-08-06T01:19:47Z",
      "cve": "CVE-2026-43490",
      "id": "CVE-2026-43490",
      "initial_release_date": "2026-05-16T01:11:57Z",
      "product_status:known_affected": "30",
      "product_status:known_not_affected": "263",
      "product_status:recommended": "4",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-43490",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-43490.json",
      "version": "6"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.