CVE-2026-68124 | 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 r
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).
- 🔗 git.kernel.org/stable/c/64b96ae7912244d55257aa330d9569ee…
- 🔗 git.kernel.org/stable/c/36dc6d6964a3b90411cc7944cd9b8b6f…
- 🔗 git.kernel.org/stable/c/68819427bc07eca7963a9e8be19e5272…
- 🔗 git.kernel.org/stable/c/f80ba170d7b3a44e3d244a2c8e06031d…
- 🔗 git.kernel.org/stable/c/06a6b606129c8a25cd457760f5370f3f…
- 🔗 git.kernel.org/stable/c/793b9b729f1e8de57be8c8daf1a9838b…
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CVE-2026-68124 | 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 r
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