mctp: serial: handle zero-length frames to prevent rx buffer overflow

{
  "id": "eecbb19fb3e46a9e4141ec27f4be46fcd4b30c6cb14224c9c3381fde3f76f031",
  "url": "https://osv.dev/vulnerability/CVE-2026-68124",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mctp: serial: handle zero-length frames to prevent rx buffer overflow",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: mctp: serial: handle zero-length frames to prevent rx buffer overflow The MCTP serial receive state machine reads a frame length byte in mctp_serial_push_header() case 2 and validates it upper-bound-only: if (c > MCTP_SERIAL_FRAME_MTU) { dev->rxstate = STATE_ERR; } else { dev->rxlen = c; dev->rxpos = 0; dev->rxstate = STATE_DATA; ... } A length of zero passes this check, so rxlen is set to 0 and the state machine advances to STATE_DATA. In mctp_serial_push() STATE_DATA, the incoming byte is stored and rxpos incremented before the terminator is dev->rxbuf[dev->rxpos] = c; dev->rxpos++; dev->rxstate = STATE_DATA; if (dev->rxpos == dev->rxlen) { dev->rxpos = 0; dev->rxstate = STATE_TRAILER; } With rxlen == 0 the \"rxpos == rxlen\" terminator can never fire (rxpos is already 1 on the first data byte), so subsequent bytes are written past the end of the fixed 74-byte rxbuf, which is the last member of the netdev private area. Every following data byte is an attacker-controlled 1-byte out-of-bounds heap write, and the overflow continues until a frame (0x7e) or escape byte resets the parser -- effectively unbounded. Reaching this requires CAP_NET_ADMIN to attach the N_MCTP line discipline and bring the resulting mctpserialN netdev up, after which the bytes arrive via the tty receive path. Route a zero-length frame straight to STATE_TRAILER instead of STATE_DATA. The trailer/framing bytes are still consumed, and the fr",
    "evidence": "osv:CVE-2026-68124",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.183",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.148",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.101",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.42",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.1.6",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-68124",
      "aliases": [
        "CVE-2026-68124"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd"
                },
                {
                  "fixed": "64b96ae7912244d55257aa330d9569ee0a8f8d99"
                },
                {
                  "fixed": "36dc6d6964a3b90411cc7944cd9b8b6f67b9807b"
                },
                {
                  "fixed": "68819427bc07eca7963a9e8be19e5272cc29186c"
                },
                {
                  "fixed": "f80ba170d7b3a44e3d244a2c8e06031d61bf3b23"
                },
                {
                  "fixed": "06a6b606129c8a25cd457760f5370f3ff01fe05d"
                },
                {
                  "fixed": "793b9b729f1e8de57be8c8daf1a9838be96cabed"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-68124.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.17.0"
                },
                {
                  "fixed": "6.1.183"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.148"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.101"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.42"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.1.6"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-68124.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:40.381023618Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/06a6b606129c8a25cd457760f5370f3ff01fe05d",
        "https://git.kernel.org/stable/c/36dc6d6964a3b90411cc7944cd9b8b6f67b9807b",
        "https://git.kernel.org/stable/c/64b96ae7912244d55257aa330d9569ee0a8f8d99",
        "https://git.kernel.org/stable/c/68819427bc07eca7963a9e8be19e5272cc29186c",
        "https://git.kernel.org/stable/c/793b9b729f1e8de57be8c8daf1a9838be96cabed",
        "https://git.kernel.org/stable/c/f80ba170d7b3a44e3d244a2c8e06031d61bf3b23",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68124.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-68124",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68124.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-68124",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 507835,
  "published_at": "2026-08-10T11:58:44.997+00:00"
}