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CVE-2026-68124 Affecting linux-6.12 package, versions <6.12.101-1~deb12u1

Severity

 Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.34% (28th percentile)

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  • Snyk IDSNYK-ECHOLATEST-LINUX612-18912453
  • published18 Aug 2026
  • disclosed10 Aug 2026
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Introduced: 10 Aug 2026

CVE-2026-68124  (opens in a new tab)

How to fix?

Upgrade Echo:latest linux-6.12 to version 6.12.101-1~deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-6.12 package and not the linux-6.12 package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

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 &gt; MCTP_SERIAL_FRAME_MTU) {
    dev-&gt;rxstate = STATE_ERR;
} else {
    dev-&gt;rxlen = c;
    dev-&gt;rxpos = 0;
    dev-&gt;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-&gt;rxbuf[dev-&gt;rxpos] = c;
dev-&gt;rxpos++;
dev-&gt;rxstate = STATE_DATA;
if (dev-&gt;rxpos == dev-&gt;rxlen) {
    dev-&gt;rxpos = 0;
    dev-&gt;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 Base Scores

version 3.1