{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-68124",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2026-68124"
  ],
  "published": "2026-08-10T12:08:00Z",
  "summary": "mctp: serial: handle zero-length frames to prevent rx buffer overflow",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmctp: serial: handle zero-length frames to prevent rx buffer overflow\n\nThe MCTP serial receive state machine reads a frame length byte in\nmctp_serial_push_header() case 2 and validates it upper-bound-only:\n\n\tif (c > MCTP_SERIAL_FRAME_MTU) {\n\t\tdev->rxstate = STATE_ERR;\n\t} else {\n\t\tdev->rxlen = c;\n\t\tdev->rxpos = 0;\n\t\tdev->rxstate = STATE_DATA;\n\t\t...\n\t}\n\nA length of zero passes this check, so rxlen is set to 0 and the state\nmachine advances to STATE_DATA. In mctp_serial_push() STATE_DATA, the\nincoming byte is stored and rxpos incremented before the terminator is\n\n\tdev->rxbuf[dev->rxpos] = c;\n\tdev->rxpos++;\n\tdev->rxstate = STATE_DATA;\n\tif (dev->rxpos == dev->rxlen) {\n\t\tdev->rxpos = 0;\n\t\tdev->rxstate = STATE_TRAILER;\n\t}\n\nWith rxlen == 0 the \"rxpos == rxlen\" terminator can never fire (rxpos is\nalready 1 on the first data byte), so subsequent bytes are written past\nthe end of the fixed 74-byte rxbuf, which is the last member of the\nnetdev private area. Every following data byte is an attacker-controlled\n1-byte out-of-bounds heap write, and the overflow continues until a\nframe (0x7e) or escape byte resets the parser -- effectively unbounded.\n\nReaching this requires CAP_NET_ADMIN to attach the N_MCTP line\ndiscipline and bring the resulting mctpserialN netdev up, after which\nthe bytes arrive via the tty receive path.\n\nRoute a zero-length frame straight to STATE_TRAILER instead of\nSTATE_DATA. The trailer/framing bytes are still consumed, and the frame\nresolves to a zero-length skb that the MCTP core rejects; the parser\nnever enters STATE_DATA with rxlen == 0, so the out-of-bounds write can\nno longer occur.\n\nKASAN, on a frame of 0x7e 0x01 0x00 followed by data bytes (before this\nchange):\n\n  UBSAN: array-index-out-of-bounds in drivers/net/mctp/mctp-serial.c:370\n  index 74 is out of range for type 'u8 [74]'\n  BUG: KASAN: slab-out-of-bounds in mctp_serial_tty_receive_buf\n  Write of size 1 at addr ... by task kworker/u16:0\n   mctp_serial_tty_receive_buf\n   tty_ldisc_receive_buf\n   flush_to_ldisc\n  Allocated by task 152:\n   alloc_netdev_mqs\n   mctp_serial_open\n\nv2: route zero-length frames to STATE_TRAILER instead of STATE_ERR so\n    the trailer/framing bytes are still consumed (Jeremy Kerr).\n\nFound by 0sec automated security-research tooling (https://0sec.ai).",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
      },
      "versions": [
        "1:6.1.47-1+rpt4"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-2712",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v6",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v8",
            "binary_version": "1:6.1.47-1+rpt4"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.1.47-1+rpt4": {
            "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e",
            "upstream_version": "6.1.47",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.1.183",
            "compiled_filter": false
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-68124"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/64b96ae7912244d55257aa330d9569ee0a8f8d99"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/36dc6d6964a3b90411cc7944cd9b8b6f67b9807b"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/68819427bc07eca7963a9e8be19e5272cc29186c"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/f80ba170d7b3a44e3d244a2c8e06031d61bf3b23"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/06a6b606129c8a25cd457760f5370f3ff01fe05d"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/793b9b729f1e8de57be8c8daf1a9838be96cabed"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-19T16:47:12Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 9.6,
      "cvss_v3_severity": "Critical",
      "scenario": "AV:A - The bug is triggered in mctp_serial_tty_receive_buf() by crafted DSP0253 serial frames; on BMC/datacenter systems MCTP-over-serial links management controllers on a shared management LAN, letting an adjacent unauthenticated peer inject 0x7e/0x01/0x00 frames without using host syscalls.\nAC:L - Exploitation is deterministic: a zero-length length byte bypasses the upper-bound check, then each following serial byte is a controlled 1-byte heap OOB write until 0x7e/0x7d resets the parser; no races or attacker-uncontrollable memory layout are required.\nPR:N - Triggering the overflow only requires delivering malicious serial bytes to an already-configured, running mctpserial netdev; a remote/adjacent MCTP peer or compromised management controller needs no Linux host credentials, CAP_NET_ADMIN, or root on the victim.\nUI:N - No victim user action is required at exploit time; administrative enablement of MCTP serial is deployment configuration, not end-user interaction under CVSS.\nS:C - Kconfig documents virtio-serial VM interconnect for MCTP serial; a malicious guest sending crafted frames to the host-side mctpserial binding can corrupt host kernel heap memory, crossing the guest/host virtualization security boundary.\nC:H - Each overflow byte is attacker-controlled and the write stream is effectively unbounded past the 74-byte rxbuf (last netdev private field), enabling slab-out-of-bounds corruption that can be leveraged for arbitrary kernel memory disclosure.\nI:H - Sustained attacker-controlled out-of-bounds heap writes can corrupt adjacent kmalloc objects, function pointers, and netdev state, providing a standard path to arbitrary kernel write and privilege-escalating code execution.\nA:H - KASAN/UBSAN report slab-out-of-bounds and array-index-out-of-bounds in mctp_serial_tty_receive_buf via flush_to_ldisc; continued overflow reliably causes kernel oops/panic or hang during tty receive processing."
    }
  }
}