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CVE PROGRAM SOURCE RECORD9.6 Critical

CVE-2026-68124

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

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Status
Published
Published
Updated
Assigning organization
Linux

Description

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 frame resolves to a zero-length skb that the MCTP core rejects; the parser never enters STATE_DATA with rxlen == 0, so the out-of-bounds write can no longer occur. KASAN, on a frame of 0x7e 0x01 0x00 followed by data bytes (before this change): UBSAN: array-index-out-of-bounds in drivers/net/mctp/mctp-serial.c:370 index 74 is out of range for type 'u8 [74]' BUG: KASAN: slab-out-of-bounds in mctp_serial_tty_receive_buf Write of size 1 at addr ... by task kworker/u16:0 mctp_serial_tty_receive_buf tty_ldisc_receive_buf flush_to_ldisc Allocated by task 152: alloc_netdev_mqs mctp_serial_open v2: route zero-length frames to STATE_TRAILER instead of STATE_ERR so the trailer/framing bytes are still consumed (Jeremy Kerr). Found by 0sec automated security-research tooling (https://0sec.ai).

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd to < 64b96ae7912244d55257aa330d9569ee0a8f8d99affected
  • a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd to < 36dc6d6964a3b90411cc7944cd9b8b6f67b9807baffected
  • a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd to < 68819427bc07eca7963a9e8be19e5272cc29186caffected
  • a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd to < f80ba170d7b3a44e3d244a2c8e06031d61bf3b23affected
  • a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd to < 06a6b606129c8a25cd457760f5370f3ff01fe05daffected
  • a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd to < 793b9b729f1e8de57be8c8daf1a9838be96cabedaffected

Linux Linux

Default version status: affected

  • 5.17affected
  • 0 to < 5.17unaffected
  • 6.1.183 to ≤ 6.1.*unaffected
  • 6.6.148 to ≤ 6.6.*unaffected
  • 6.12.101 to ≤ 6.12.*unaffected
  • 6.18.42 to ≤ 6.18.*unaffected
  • 7.1.6 to ≤ 7.1.*unaffected
  • 7.2 to ≤ *unaffected

References