CVE-2026-63909 (GCVE-0-2026-63909)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-20 13:41
VLAI
Title
ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 282cbbb476b9f35793452bc461934af4c7eca169 , < 5500ba1d410aed1eded3eb04a76b10cfb4409334 (git)
Affected: f20adc4ef7428bc485ee83fd1a592252fb87718b , < f6324b4240cf0b26a84c33f68a1222d727ff4af2 (git)
Affected: 325d4ac11f526cb8964cff14548ccf02d8c756d8 , < 0fe08c5776a798f46df1fd74b331be26bdd644d6 (git)
Affected: 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c , < d333af32e4451285e427f2d9c29de3a39f6f6d48 (git)
Affected: 90089584b2e25c4510b7b987387b4405f0673ece , < 94215d55b09445993929f4fc966061d61de74929 (git)
Affected: 151b1799861fde38087c08f613abc2843ef597b0 , < 4f7c131d2bdd7cd64b96f60d10be5ea72253f520 (git)
Affected: d07b26f39246a82399661936dd0c853983cfade7 , < 0e60dafe97eca61721f3db456f97d97a80c6c8ae (git)
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Linux Linux Affected: 6.6.140 , < 6.6.143 (semver)
Affected: 6.12.84 , < 6.12.93 (semver)
Affected: 6.18.25 , < 6.18.35 (semver)
Affected: 7.0.2 , < 7.0.12 (semver)
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{
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          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smbacl.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops\n\nCommit d07b26f39246 (\"ksmbd: require minimum ACE size in\nsmb_check_perm_dacl()\") introduced a transposed bounds check:\n\n    if (offsetof(struct smb_ace, sid) + aces_size \u003c CIFS_SID_BASE_SIZE)\n\nSince offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates\nto `aces_size \u003c 0`. Because `aces_size` is always non-negative, this\ncheck becomes dead code and never breaks the loop.\n\nWorse, that commit removed the old 4-byte guard, meaning the loop now\nreads `ace-\u003esize` (offset 2) even when `aces_size` is 0-3 bytes. This\nre-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation\nduring subsequent SMB2_CREATE operations.\n\nFix this by properly transposing the comparison to require at least\n16 bytes (8-byte offset + 8-byte SID base), matching the correct form\nused in smb_inherit_dacl()."
        }
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    "cveId": "CVE-2026-63909",
    "datePublished": "2026-07-19T14:55:15.060Z",
    "dateReserved": "2026-07-19T07:54:57.020Z",
    "dateUpdated": "2026-07-20T13:41:19.196Z",
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-21T11:37:13+00:00",
      "cve": "CVE-2026-63909",
      "id": "CVE-2026-63909",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_not_affected": "275",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63909.json",
      "version": "3"
    }
  }
}



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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

Author Source Type Date Other

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.