---
cve: "CVE-2026-68124"
severity: "CRITICAL"
cvss: 9.6
epss: "35%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-08-10 13:19:57"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-07T09:52:36+02:00"
---

# CVE-2026-68124

> 9.6 CRITICAL

## Beschreibung

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).

## CVSS-Vektor

```
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Benachbart | warn |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Verändert | bad |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- Kernel ≥ 6.1.183
- Kernel ≥ 6.6.148
- Kernel ≥ 6.12.101
- Kernel ≥ 6.18.42
- Kernel ≥ 7.1.6

## Referenzen

- <https://git.kernel.org/stable/c/64b96ae7912244d55257aa330d9569ee0a8f8d99>
- <https://git.kernel.org/stable/c/36dc6d6964a3b90411cc7944cd9b8b6f67b9807b>
- <https://git.kernel.org/stable/c/68819427bc07eca7963a9e8be19e5272cc29186c>
- <https://git.kernel.org/stable/c/f80ba170d7b3a44e3d244a2c8e06031d61bf3b23>
- <https://git.kernel.org/stable/c/06a6b606129c8a25cd457760f5370f3ff01fe05d>
- <https://git.kernel.org/stable/c/793b9b729f1e8de57be8c8daf1a9838be96cabed>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-68124) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_