FKIE_CVE-2026-89638

Vulnerability from fkie_nvd - Published: 2026-09-11 20:19 - Updated: 2026-10-30 13:20
Severity
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: clear setuid/setgid bit on write with cifsacl/modefromsid/posix extensions When a file has the setuid or setgid bit set and is written to, the VFS strips those bits and issues a setattr with ATTR_KILL_SUID/ATTR_KILL_SGID together with an ATTR_MODE carrying the already-cleared mode. Both cifs_setattr_unix() and cifs_setattr_nounix() unconditionally dropped ATTR_MODE in that case: /* skip mode change if it's just for clearing setuid/setgid */ if (attrs->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) attrs->ia_valid &= ~ATTR_MODE; This is fine for the default mount, where the mode is only emulated via the DOS read-only attribute and cannot represent the setuid/setgid bits anyway. However, with the "cifsacl" or "modefromsid" mount options the mode is stored on the server through an ACL (id_mode_to_cifs_acl()), with the SMB3.1.1 POSIX extensions the mode is sent to the server directly, and with the SMB1 Unix extensions (cifs_setattr_unix) the mode is sent via CIFSSMBUnixSetPathInfo(). In all those cases dropping ATTR_MODE means the cleared mode is never pushed to the server, so the setuid/setgid bit survives the write. This is a security issue: on local filesystems the setuid bit is stripped when a file is written, but over these cifs.ko mounts the bit persists on the server, potentially allowing an unexpected privilege escalation on subsequent execution. Fix this in two places: 1. cifs_setattr_nounix(): only take the "skip mode change" shortcut when the mode is emulated via the DOS read-only attribute (i.e. neither cifsacl/modefromsid nor the SMB3.1.1 POSIX extensions are in effect), so that the cleared mode is propagated to the server in the ACL / POSIX cases. 2. cifs_setattr_unix(): this function is only called when Unix extensions are in effect, so the mode is always stored on the server. Remove the shortcut entirely so that the cleared mode is always pushed.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/2a5206992f526178881e8f5c4644757c336fb76d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/58b23fc9fb580432470d6c5da3c1e5660dba9fbc
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/69bfe810ecd1e0387d8975d711cd326341d13c6e
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7ceb6f7cb8f8f2b094e0dcdaf75757775d231378
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a3a0cc83761e46a75b1ed6bfaf35961f2c211148
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b10015807e4c628095d1d1d1c9307efc8cdd9e1b
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b8e5dc4f95e5484159b343903f302eb6d783f2e6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ce0e675907b887db2b1e44a806118b0a7d8b6b18
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/inode.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "ce0e675907b887db2b1e44a806118b0a7d8b6b18",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "a3a0cc83761e46a75b1ed6bfaf35961f2c211148",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "2a5206992f526178881e8f5c4644757c336fb76d",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "7ceb6f7cb8f8f2b094e0dcdaf75757775d231378",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "58b23fc9fb580432470d6c5da3c1e5660dba9fbc",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "b10015807e4c628095d1d1d1c9307efc8cdd9e1b",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "69bfe810ecd1e0387d8975d711cd326341d13c6e",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            },
            {
              "lessThan": "b8e5dc4f95e5484159b343903f302eb6d783f2e6",
              "status": "affected",
              "version": "d32c4f2626acc385d5187bd5c0c24f442328dc60",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/inode.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.24"
            },
            {
              "lessThan": "2.6.24",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.273",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.224",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.191",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.160",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.113",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: clear setuid/setgid bit on write with cifsacl/modefromsid/posix extensions\n\nWhen a file has the setuid or setgid bit set and is written to, the VFS\nstrips those bits and issues a setattr with ATTR_KILL_SUID/ATTR_KILL_SGID\ntogether with an ATTR_MODE carrying the already-cleared mode.\n\nBoth cifs_setattr_unix() and cifs_setattr_nounix() unconditionally dropped\nATTR_MODE in that case:\n\n\t/* skip mode change if it\u0027s just for clearing setuid/setgid */\n\tif (attrs-\u003eia_valid \u0026 (ATTR_KILL_SUID|ATTR_KILL_SGID))\n\t\tattrs-\u003eia_valid \u0026= ~ATTR_MODE;\n\nThis is fine for the default mount, where the mode is only emulated via\nthe DOS read-only attribute and cannot represent the setuid/setgid bits\nanyway.  However, with the \"cifsacl\" or \"modefromsid\" mount options the\nmode is stored on the server through an ACL (id_mode_to_cifs_acl()), with\nthe SMB3.1.1 POSIX extensions the mode is sent to the server directly,\nand with the SMB1 Unix extensions (cifs_setattr_unix) the mode is sent\nvia CIFSSMBUnixSetPathInfo().  In all those cases dropping ATTR_MODE means\nthe cleared mode is never pushed to the server, so the setuid/setgid bit\nsurvives the write.\n\nThis is a security issue: on local filesystems the setuid bit is stripped\nwhen a file is written, but over these cifs.ko mounts the bit persists on\nthe server, potentially allowing an unexpected privilege escalation on\nsubsequent execution.\n\nFix this in two places:\n\n  1. cifs_setattr_nounix(): only take the \"skip mode change\" shortcut\n     when the mode is emulated via the DOS read-only attribute (i.e.\n     neither cifsacl/modefromsid nor the SMB3.1.1 POSIX extensions are\n     in effect), so that the cleared mode is propagated to the server\n     in the ACL / POSIX cases.\n\n  2. cifs_setattr_unix(): this function is only called when Unix\n     extensions are in effect, so the mode is always stored on the\n     server.  Remove the shortcut entirely so that the cleared mode is\n     always pushed."
    }
  ],
  "id": "CVE-2026-89638",
  "lastModified": "2026-10-30T13:20:23.393",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-89638",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-10-16T19:24:50.502778Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-09-11T20:19:49.493",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/2a5206992f526178881e8f5c4644757c336fb76d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/58b23fc9fb580432470d6c5da3c1e5660dba9fbc"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/69bfe810ecd1e0387d8975d711cd326341d13c6e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7ceb6f7cb8f8f2b094e0dcdaf75757775d231378"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a3a0cc83761e46a75b1ed6bfaf35961f2c211148"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b10015807e4c628095d1d1d1c9307efc8cdd9e1b"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b8e5dc4f95e5484159b343903f302eb6d783f2e6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ce0e675907b887db2b1e44a806118b0a7d8b6b18"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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