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ksmbd: require minimum ACE size in smb_check_perm_dacl()

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: ksmbd: require minimum ACE size in smb_check_perm_dacl() Both ACE-walk loops in smb_check_perm_dacl() only guard against an under-sized remaining buffer, not against an ACE whose declared `ace->size` is smaller than the struct it claims to describe: if (offsetof(struct smb_ace, access_req) > aces_size) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size) break; The first check only requires the 4-byte ACE header to be in bounds; it does not require access_req (4 bytes at offset 4) to be readable. An attacker who has set a crafted DACL on a file they own can declare ace->size == 4 with aces_size == 4, pass both checks, and then granted |= le32_to_cpu(ace->access_req); /* upper loop */ compare_sids(&sid, &ace->sid); /* lower loop */ reads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at offset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES * 4 bytes). Tighten both loops to require ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE which is the smallest valid on-wire ACE layout (4-byte header + 4-byte access_req + 8-byte sid base with zero sub-auths). Also reject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES before letting compare_sids() dereference sub_auth[] entries. parse_sec_desc() already enforces an equivalent check (lines 441-448); smb_check_perm_dacl() simply grew weaker validation over time. Reachability: authenticated SMB client with pe

Announced Source revision 1
Original source ↗

CVE-2026-31712

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-2026-31712

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": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "282cbbb476b9f35793452bc461934af4c7eca169",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "f20adc4ef7428bc485ee83fd1a592252fb87718b",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "325d4ac11f526cb8964cff14548ccf02d8c756d8",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "90089584b2e25c4510b7b987387b4405f0673ece",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "151b1799861fde38087c08f613abc2843ef597b0",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
        "lessThan": "d07b26f39246a82399661936dd0c853983cfade7",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "fs/smb/server/smbacl.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "5.15"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "5.15",
        "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": "6.12.84",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.25",
        "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/server/smbacl.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-31712

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#28317 · Revision 1
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Publisher date
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