CVE-2026-43350 (GCVE-0-2026-43350)
Vulnerability from cvelistv5
Published
2026-05-08 13:41
Modified
2026-08-05 12:27
Severity ?
7.6 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: require a full NFS mode SID before reading mode bits parse_dacl() treats an ACE SID matching sid_unix_NFS_mode as an NFS mode SID and reads sid.sub_auth[2] to recover the mode bits. That assumes the ACE carries three subauthorities, but compare_sids() only compares min(a, b) subauthorities. A malicious server can return an ACE with num_subauth = 2 and sub_auth[] = {88, 3}, which still matches sid_unix_NFS_mode and then drives the sub_auth[2] read four bytes past the end of the ACE. Require num_subauth >= 3 before treating the ACE as an NFS mode SID. This keeps the fix local to the special-SID mode path without changing compare_sids() semantics for the rest of cifsacl.
References
Impacted products
Vendor Product Version
Linux Linux Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
Version: e2f8fbfb8d09c06decde162090fac3ee220aa280
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/cifsacl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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          "product": "Linux",
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "5.4"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "5.10.259",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.210",
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              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.175",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "6.6.136",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.84",
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            },
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.25",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.2",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.259",
                  "versionStartIncluding": "5.4",
                  "vulnerable": true
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                  "vulnerable": true
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.136",
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                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                },
                {
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                  "versionEndExcluding": "7.1",
                  "versionStartIncluding": "5.4",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: require a full NFS mode SID before reading mode bits\n\nparse_dacl() treats an ACE SID matching sid_unix_NFS_mode as an NFS\nmode SID and reads sid.sub_auth[2] to recover the mode bits.\n\nThat assumes the ACE carries three subauthorities, but compare_sids()\nonly compares min(a, b) subauthorities.  A malicious server can return\nan ACE with num_subauth = 2 and sub_auth[] = {88, 3}, which still\nmatches sid_unix_NFS_mode and then drives the sub_auth[2] read four\nbytes past the end of the ACE.\n\nRequire num_subauth \u003e= 3 before treating the ACE as an NFS mode SID.\nThis keeps the fix local to the special-SID mode path without changing\ncompare_sids() semantics for the rest of cifsacl."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.6,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable SMB client parser consumes ACL/security-descriptor data returned over the network by an SMB server. A malicious or compromised remote SMB server can supply the short NFS mode SID in a query-info/query-security response.\nAC:L - Once a CIFS/SMB mount uses the modefromsid path, triggering is deterministic: the server only needs to return an ACE with num_subauth=2 matching S-1-5-88-3 and arrange it at the relevant boundary. There is no race or condition outside the attacker\u0027s control.\nPR:N - The attacker is the remote SMB server or controls the server response and needs no privileges on the vulnerable client system. Any SMB authentication is chosen or satisfied by the attacker-controlled server side.\nUI:R - The client must mount or access the SMB share so that lookup/stat/revalidation requests fetch and parse the malicious ACL. That requires victim-side user or administrator action such as mounting or opening/statting files on the share.\nS:U - The impact remains within the Linux client kernel and its mounted SMB filesystem state. There is no VM escape, sandbox boundary crossing, or separate security authority transition.\nC:L - The bug is a bounded four-byte out-of-bounds read past the advertised ACE SID, and the read value can influence mode bits visible through inode metadata. This is limited disclosure rather than an arbitrary kernel memory read.\nI:L - The out-of-bounds value is applied as POSIX mode bits for the SMB inode, allowing limited corruption of client-side permission metadata. It does not provide an arbitrary write or direct control-flow corruption primitive.\nA:H - The malformed server-controlled security descriptor can drive an out-of-bounds kernel read in the SMB client during ordinary metadata refresh, and such kernel memory faults are defensibly treated as possible kernel oops/panic. The trigger can be repeated by causing further lookups or stat/revalidation operations."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:27:24.940Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/23b54d6cc3ef30a51d984dc74364f24039ae2ecb"
        },
        {
          "url": "https://git.kernel.org/stable/c/1592a6cd6f653f2d24572a6976c7a775b19f4940"
        },
        {
          "url": "https://git.kernel.org/stable/c/8bd4cad3f458d11650d51c2d24b03fb1770ae6cc"
        },
        {
          "url": "https://git.kernel.org/stable/c/b53b8e98c23310294fc45fc686db5ee860311896"
        },
        {
          "url": "https://git.kernel.org/stable/c/c8eef12af1cc73031639ea7cf16e0b10e2536b0b"
        },
        {
          "url": "https://git.kernel.org/stable/c/38a69f08ee82c450d3e4168707fff2e317dc3ff7"
        },
        {
          "url": "https://git.kernel.org/stable/c/f8488c07bea2431ee12a6067d736578064fa46b4"
        },
        {
          "url": "https://git.kernel.org/stable/c/2757ad3e4b6f9e0fed4c7739594e702abc5cab21"
        }
      ],
      "title": "smb: client: require a full NFS mode SID before reading mode bits",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-43350",
    "datePublished": "2026-05-08T13:41:53.276Z",
    "dateReserved": "2026-05-01T14:12:56.003Z",
    "dateUpdated": "2026-08-05T12:27:24.940Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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