CVE-2026-98171 (GCVE-0-2026-98171)

Vulnerability from cvelistv5 – Published: 2026-10-06 08:44 – Updated: 2026-10-07 06:49
VLAI
Title
smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs Fix several related bounds checking and pointer lifecycle issues in receive_encrypted_standard()'s handling of compound encrypted frames: - Clear next_buffer after assigning it to server->bigbuf. A stale next_buffer pointer can lead to a use-after-free on subsequent error paths. - Update pdu_length to the decrypted plaintext size (buf_size). Using the pre-decryption length allows NextCommand to point into stale ciphertext residue. - Reject next_cmd values smaller than MID_HEADER_SIZE(server). - Fix an integer overflow in the upper bound check by verifying pdu_length - next_cmd < MID_HEADER_SIZE(server), ensuring the trailing slice is large enough for a header.
Severity
8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 54/100 over 6619 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: b24df3e30cbf48255db866720fb71f14bf9d2f39 , < 72eaef1f37a3b6bec11c342736834dc3707be3e4 (git)
Affected: b24df3e30cbf48255db866720fb71f14bf9d2f39 , < 491e33144dee872cffda207f6fcb09260728f803 (git)
Affected: b24df3e30cbf48255db866720fb71f14bf9d2f39 , < 8749946579708ea0d339034bb7f423a67dbe89cf (git)
Affected: b24df3e30cbf48255db866720fb71f14bf9d2f39 , < 96c436e4b010711452b2872558938f4ef276492a (git)
Affected: b24df3e30cbf48255db866720fb71f14bf9d2f39 , < 858d5ac22cb889266993e7670f9f0c4f4aeedd78 (git)
Affected: b24df3e30cbf48255db866720fb71f14bf9d2f39 , < 05762c5bc1cfdcac36747994fde2c04387a457f1 (git)
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Linux Linux Affected: 4.19
Unaffected: 0 , < 4.19 (semver)
Unaffected: 6.1.189 , ≤ 6.1.* (semver)
Unaffected: 6.6.158 , ≤ 6.6.* (semver)
Unaffected: 6.12.112 , ≤ 6.12.* (semver)
Unaffected: 6.18.54 , ≤ 6.18.* (semver)
Unaffected: 7.2.8 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc4 , ≤ * (original_commit_for_fix)
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs\n\nFix several related bounds checking and pointer lifecycle issues in\nreceive_encrypted_standard()\u0027s handling of compound encrypted frames:\n\n- Clear next_buffer after assigning it to server-\u003ebigbuf. A stale\n  next_buffer pointer can lead to a use-after-free on subsequent\n  error paths.\n- Update pdu_length to the decrypted plaintext size (buf_size). Using\n  the pre-decryption length allows NextCommand to point into stale\n  ciphertext residue.\n- Reject next_cmd values smaller than MID_HEADER_SIZE(server).\n- Fix an integer overflow in the upper bound check by verifying\n  pdu_length - next_cmd \u003c MID_HEADER_SIZE(server), ensuring the\n  trailing slice is large enough for a header."
        }
      ],
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
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              "value": "AV:N - The malformed input is an encrypted SMB2 compound response (TRANSFORM header, inner NextCommand chain) sent by the SMB server over TCP/445 and parsed by receive_encrypted_standard() via cifs_demultiplex_thread -\u003e smb3_receive_transform, so the bytes that cause the bug arrive over a routable network protocol.\nAC:L - The malicious server fully controls the sequence: a compound response whose first PDU has non-zero NextCommand, then a trailing PDU with NextCommand=0 and STATUS_PENDING or an unmatched MID with a bad header makes cifs_handle_standard() return non-zero, freeing the stale next_buffer every time; no race or external state is involved.\nPR:N - The attacker is the SMB server endpoint. It needs no account or privilege on the victim client, because it negotiates the session and encryption keys itself and so can produce valid encrypted frames.\nUI:R - A victim user or admin has to mount (or be redirected by DFS to) a share hosted on the attacker-controlled server before the client receives any encrypted compound response, so user action is required.\nS:U - The corruption is confined to the client kernel\u0027s own cifs receive buffers and slab/mempool objects, which is a standard kernel compromise and does not cross into a separate security authority.\nC:H - The error path frees server-\u003esmallbuf/bigbuf while it is still installed, which is a UAF on a kernel heap object. The object can be reallocated and its contents processed as SMB responses, a primitive usable for kernel memory disclosure.\nI:H - After the bad free, allocate_buffers() keeps the dangling smallbuf/bigbuf, and cifs_read_from_socket() writes the next frame\u0027s server-chosen bytes into the freed object (with a later double free), giving an attacker-controlled write into reallocated kernel memory.\nA:H - The use-after-free and double free of the cifs receive buffers in the demultiplex thread can corrupt the slab or mempool, causing a kernel oops or panic on the client and making every mount on that host unavailable."
            }
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        "shortName": "Linux"
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        {
          "url": "https://git.kernel.org/stable/c/05762c5bc1cfdcac36747994fde2c04387a457f1"
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      "title": "smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98171",
    "datePublished": "2026-10-06T08:44:15.927Z",
    "dateReserved": "2026-09-25T10:25:14.322Z",
    "dateUpdated": "2026-10-07T06:49:20.472Z",
    "state": "PUBLISHED"
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs\n\nFix several related bounds checking and pointer lifecycle issues in\nreceive_encrypted_standard()\u0027s handling of compound encrypted frames:\n\n- Clear next_buffer after assigning it to server-\u003ebigbuf. A stale\n  next_buffer pointer can lead to a use-after-free on subsequent\n  error paths.\n- Update pdu_length to the decrypted plaintext size (buf_size). Using\n  the pre-decryption length allows NextCommand to point into stale\n  ciphertext residue.\n- Reject next_cmd values smaller than MID_HEADER_SIZE(server).\n- Fix an integer overflow in the upper bound check by verifying\n  pdu_length - next_cmd \u003c MID_HEADER_SIZE(server), ensuring the\n  trailing slice is large enough for a header."
          }
        ],
        "id": "CVE-2026-98171",
        "lastModified": "2026-10-07T07:17:03.600",
        "metrics": {
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              "cvssData": {
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                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 8.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
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        "vulnStatus": "Received"
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      "current_release_date": "2026-10-09T16:54:07Z",
      "cve": "CVE-2026-98171",
      "id": "CVE-2026-98171",
      "initial_release_date": "2026-10-07T16:28:36Z",
      "product_status:known_affected": "341",
      "product_status:known_not_affected": "6",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-98171",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-98171.json",
      "version": "3"
    }
  }
}



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