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smb: client: validate the whole DACL before rewriting it in cifsacl

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: smb: client: validate the whole DACL before rewriting it in cifsacl build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a server-supplied dacloffset and then use the incoming ACL to rebuild the chmod/chown security descriptor. The original fix only checked that the struct smb_acl header fits before reading dacl_ptr->size or dacl_ptr->num_aces. That avoids the immediate header-field OOB read, but the rewrite helpers still walk ACEs based on pdacl->num_aces with no structural validation of the incoming DACL body. A malicious server can return a truncated DACL that still contains a header, claims one or more ACEs, and then drive replace_sids_and_copy_aces() or set_chmod_dacl() past the validated extent while they compare or copy attacker-controlled ACEs. Factor the DACL structural checks into validate_dacl(), extend them to validate each ACE against the DACL bounds, and use the shared validator before the chmod/chown rebuild paths. parse_dacl() reuses the same validator so the read-side parser and write-side rewrite paths agree on what constitutes a well-formed incoming DACL.

Announced Source revision 1
Original source ↗

CVE-2026-31709

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-31709

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "b8603d9ae6c9087662b098619996bc4a8064319d",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "c2abdebf72000a64603ced84d36ccbd164f11391",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "d92f3f0b22414e7515696a02224d0af55e3004a3",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "b78db9bddc84136f6a0bb49e8883cf200dfb87a8",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4",
        "lessThan": "0a8cf165566ba55a39fd0f4de172119dd646d39a",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "fs/smb/client/cifsacl.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "5.12"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "5.12",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.15.210",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.176",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.140",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.86",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.35",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.0.2",
        "versionType": "semver",
        "lessThanOrEqual": "7.0.*"
      },
      {
        "status": "unaffected",
        "version": "7.1",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "fs/smb/client/cifsacl.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-31709

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#39987 · Revision 1
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Publisher date
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