{"id":"CVE-2026-68124","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-68124","generatedAt":"2026-10-28T07:04:24.518Z","title":"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…","description":"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).","published":"2026-08-10T13:19:58.000Z","lastModified":"2026-08-19T17:20:30.000Z","status":"Received","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":9.6,"severity":"CRITICAL","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"},"cwe":[],"affected":[],"epss":{"score":0.00343,"percentile":0.27678,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.34%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/06a6b606129c8a25cd457760f5370f3ff01fe05d","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/36dc6d6964a3b90411cc7944cd9b8b6f67b9807b","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/64b96ae7912244d55257aa330d9569ee0a8f8d99","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/68819427bc07eca7963a9e8be19e5272cc29186c","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/793b9b729f1e8de57be8c8daf1a9838be96cabed","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/f80ba170d7b3a44e3d244a2c8e06031d61bf3b23","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-68124","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}