CVE-2026-97559 (GCVE-0-2026-97559)
Vulnerability from cvelistv5
Published
2026-09-25 10:21
Modified
2026-10-21 12:53
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: fail DACL rewrite when the new DACL exceeds 64K replace_sids_and_copy_aces() and set_chmod_dacl() accumulate the size of the DACL they build in a u16. That accumulator can wrap. validate_dacl() caps num_aces at (dacl_size - sizeof(struct smb_acl)) / 20, i.e. 3276 for a maximally sized DACL, while each rewritten ACE can grow to sizeof(struct smb_ace) (76 bytes) once its SID is replaced with one carrying SID_MAX_SUB_AUTHORITIES sub-authorities. The worst case is therefore sizeof(struct smb_acl) + 3276 * 76 = 248984 bytes, far beyond what a u16 can hold. A wraparound is reached with 863 ACEs. After the wraparound, ndacl_ptr->size becomes meaningless and the offset will point anywhere in the ACE array. As a result, we will see corruption of the DACL, which then gets sent to the server. This is not an out-of-bounds write as the allocation now covers the worst-case expansion, so writes will always go into the buffer. Adjust the code to use a u32 internally and return -EOVERFLOW in the overflow case. The operation must be refused, because a DACL can only hold 2^16-1 bytes on the wire and larger DACLs cannot be represented. set_chmod_dacl() carries the same pattern and is fixed the same way. It only wraps once the source DACL comes within roughly 380 bytes of the 64K ceiling, but the failure mode is identical.
References
Impacted products
Vendor Product Version
Linux Linux Version: f5065508897a922327f32223082325d10b069ebc
Version: f5065508897a922327f32223082325d10b069ebc
Version: f5065508897a922327f32223082325d10b069ebc
Version: f5065508897a922327f32223082325d10b069ebc
Version: f5065508897a922327f32223082325d10b069ebc
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/cifsacl.c"
          ],
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            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/cifsacl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.12"
            },
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
              "version": "6.6.160",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.112",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.7",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.160",
                  "versionStartIncluding": "5.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
                },
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.7",
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fail DACL rewrite when the new DACL exceeds 64K\n\nreplace_sids_and_copy_aces() and set_chmod_dacl() accumulate the size of\nthe DACL they build in a u16. That accumulator can wrap.\n\nvalidate_dacl() caps num_aces at (dacl_size - sizeof(struct smb_acl)) /\n20, i.e. 3276 for a maximally sized DACL, while each rewritten ACE can\ngrow to sizeof(struct smb_ace) (76 bytes) once its SID is replaced with\none carrying SID_MAX_SUB_AUTHORITIES sub-authorities. The worst case is\ntherefore sizeof(struct smb_acl) + 3276 * 76 = 248984 bytes, far beyond\nwhat a u16 can hold. A wraparound is reached with 863 ACEs.\n\nAfter the wraparound, ndacl_ptr-\u003esize becomes meaningless and the offset\nwill point anywhere in the ACE array. As a result, we will see\ncorruption of the DACL, which then gets sent to the server. This is not\nan out-of-bounds write as the allocation now covers the worst-case\nexpansion, so writes will always go into the buffer.\n\nAdjust the code to use a u32 internally and return -EOVERFLOW in the\noverflow case. The operation must be refused, because a DACL can only\nhold 2^16-1 bytes on the wire and larger DACLs cannot be represented.\n\nset_chmod_dacl() carries the same pattern and is fixed the same way. It\nonly wraps once the source DACL comes within roughly 380 bytes of the\n64K ceiling, but the failure mode is identical."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:53:17.080Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/284877c6189fda1ac3d81771dd8482660a0c7dc1"
        },
        {
          "url": "https://git.kernel.org/stable/c/d433376abc47e10870ae732f89c7c1a60b199a0c"
        },
        {
          "url": "https://git.kernel.org/stable/c/2ef532a01f44687f5b95001e88247cf05bff9892"
        },
        {
          "url": "https://git.kernel.org/stable/c/ee13d687d06a6fbb2008625dd560c654231b28e0"
        },
        {
          "url": "https://git.kernel.org/stable/c/d05045177a855386bca5e1909e08d06290e6e3b3"
        }
      ],
      "title": "smb: client: fail DACL rewrite when the new DACL exceeds 64K",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-97559",
    "datePublished": "2026-09-25T10:21:48.866Z",
    "dateReserved": "2026-09-24T16:01:01.155Z",
    "dateUpdated": "2026-10-21T12:53:17.080Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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