CVE-2026-68124mctp: serial: handle zero-length frames to prevent rx buffer overflow

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).

Timeline

Scores

EPSS (exploitation in 30 days)

0.34% · top 72% of all CVEs (14 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.6.

Affected products

• Linux · Linux

  • affected a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd – < 64b96ae7912244d55257aa330d9569ee0a8f8d99
  • affected a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd – < 36dc6d6964a3b90411cc7944cd9b8b6f67b9807b
  • affected a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd – < 68819427bc07eca7963a9e8be19e5272cc29186c
  • affected a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd – < f80ba170d7b3a44e3d244a2c8e06031d61bf3b23
  • affected a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd – < 06a6b606129c8a25cd457760f5370f3ff01fe05d
  • affected a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd – < 793b9b729f1e8de57be8c8daf1a9838be96cabed

• Linux · Linux

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

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-55505 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-68124](https://cveledger.app/badge/CVE-2026-68124.svg)](https://cveledger.app/cve/CVE-2026-68124)

Record last updated 19 Aug 2026, 16:29 UTC.