ksmbd: fix heap out-of-bounds write in krb5_authenticate()

{
  "id": "213363e4c83f0a0be0b44f01955efb824dd411ea8c007315004709478a91bae3",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-99083",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ksmbd: fix heap out-of-bounds write in krb5_authenticate()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix heap out-of-bounds write in krb5_authenticate() In krb5_authenticate(), out_len is calculated to determine available headroom in response_buf for the incoming Kerberos AP-REP token. However, when SMB2_SESSION_SETUP is processed as a non-first element of a compounded SMB2 request, the calculation omits work->next_smb2_rsp_hdr_off. This causes out_len to overstate remaining buffer headroom by the cumulative size of prior responses in the compound chain. Consequently, the length check in ksmbd_krb5_authenticate() (*out_len <= resp->spnego_blob_len) passes erroneously, allowing memcpy() to write the AP-REP blob past the end of response_buf into adjacent kernel heap memory. Fix this by subtracting work->next_smb2_rsp_hdr_off when computing out_len, ensuring it accurately reflects physical remaining buffer space.",
    "evidence": "cve:CVE-2026-99083",
    "products": [
      {
        "name": {
          "value": "Linux",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      },
      {
        "name": {
          "value": "Linux",
          "evidence": "/containers/cna/affected/1/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-99083",
      "aliases": [
        "CVE-2026-99083"
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "version": "3.1",
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - ksmbd_conn_handler_loop() receives the compound request over TCP/445, and __process_request() dispatches its non-first SMB2 SESSION_SETUP to smb2_sess_setup() and krb5_authenticate(). The SESSION_SETUP SecurityBuffer carries the Kerberos AP-REQ that produces the AP-REP copied by the patched path.\nAC:L - The same authenticated peer can create directory entries, request a sized QUERY_DIRECTORY response, and place SESSION_SETUP later in the compound, controlling next_smb2_rsp_hdr_off before supplying its valid AP-REQ; no race or external actor is required.\nPR:L - ksmbd_krb5_authenticate() checks KSMBD_USER_FLAG_OK before its length check and memcpy; ksmbd.mountd sets it only after krb5_rd_req() accepts the AP-REQ and usm_handle_login_request() recognizes the account. An ordinary valid Kerberos account suffices, but an unauthenticated peer cannot reach the write.\nUI:N - The peer opens the session, prepares the prior compound response, and sends the Kerberos SESSION_SETUP itself; no victim user must open, mount, or approve anything.\nS:U - ksmbd_krb5_authenticate() corrupts memory adjacent to the host kernel's response_buf allocation; this remains within the same kernel security authority and crosses no VM, IOMMU, or sandbox boundary.\nC:H - The AP-REP memcpy in ksmbd_krb5_authenticate() can overrun response_buf and corrupt adjacent heap objects; exploitable kernel heap corruption can be converted into a memory-read primitive exposing arbitrary kernel data.\nI:H - The memcpy writes resp->spnego_blob_len AP-REP bytes beyond response_buf into adjacent kernel heap memory, enabling corruption of object metadata or control data and potential kernel code execution.\nA:H - Writing the AP-REP beyond response_buf can corrupt adjacent allocations or allocator metadata and trigger KASAN, an oops, or a kernel panic; the authenticated SMB peer can repeat the compound request."
            }
          ]
        }
      ],
      "affected": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "98422bdd4cb3ca4d08844046f6507d7ec2c2b8d8",
              "lessThan": "59c6dcc5dd9dafe764ca0d40525933b2be69b059",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "98422bdd4cb3ca4d08844046f6507d7ec2c2b8d8",
              "lessThan": "80af1bde97d5a85ad6f2c40ca894ccc8fa75a27a",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "98422bdd4cb3ca4d08844046f6507d7ec2c2b8d8",
              "lessThan": "517404e157395d0f8da125ca956c566895dfcd06",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "98422bdd4cb3ca4d08844046f6507d7ec2c2b8d8",
              "lessThan": "4722d06b2907585074252061b1024a696c1cfc23",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "98422bdd4cb3ca4d08844046f6507d7ec2c2b8d8",
              "lessThan": "23a0be6a84a38ac169eeab49017934e8e27c65f0",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "676392184785ace61e939831e7ca44a03d438c3b",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "ef572ffa8eb44111eed2925fbb2adca78bdcbf61",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "2ba03cecb12ac7ac9e0170e251543c56832d9959",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5.15.145",
              "lessThan": "5.16",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "6.1.40",
              "lessThan": "6.2",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "6.4.5",
              "lessThan": "6.5",
              "versionType": "semver"
            }
          ],
          "programFiles": [
            "fs/smb/server/smb2pdu.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.5"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.5",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.6.160",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.114",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.58",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.2.12",
              "versionType": "semver",
              "lessThanOrEqual": "7.2.*"
            },
            {
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "fs/smb/server/smb2pdu.c"
          ],
          "defaultStatus": "affected"
        }
      ],
      "modified": "2026-10-26T06:56:58.783Z",
      "provider": "cve",
      "references": [
        "https://git.kernel.org/stable/c/59c6dcc5dd9dafe764ca0d40525933b2be69b059",
        "https://git.kernel.org/stable/c/80af1bde97d5a85ad6f2c40ca894ccc8fa75a27a",
        "https://git.kernel.org/stable/c/517404e157395d0f8da125ca956c566895dfcd06",
        "https://git.kernel.org/stable/c/4722d06b2907585074252061b1024a696c1cfc23",
        "https://git.kernel.org/stable/c/23a0be6a84a38ac169eeab49017934e8e27c65f0"
      ],
      "provider_metadata": {
        "cna": {
          "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
          "shortName": "Linux",
          "dateUpdated": "2026-10-26T06:56:58.783Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-99083",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 263383,
  "published_at": "2026-10-23T12:45:01.735+00:00"
}