CVE-2026-68124 (GCVE-0-2026-68124)
Vulnerability from cvelistv5
Published
2026-08-10 11:58
Modified
2026-08-19 16:29
Severity ?
VLAI Severity ?
EPSS score ?
Summary
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).
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd Version: a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd Version: a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd Version: a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd Version: a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd Version: a0c2ccd9b5ad0a9e838158404e041b5a8ff762dd |
||
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"drivers/net/mctp/mctp-serial.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
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{
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"versionType": "git"
}
]
},
{
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"product": "Linux",
"programFiles": [
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],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "5.17"
},
{
"lessThan": "5.17",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.183",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.148",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.101",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.42",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.6",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.1.183",
"versionStartIncluding": "5.17",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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{
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{
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}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmctp: serial: handle zero-length frames to prevent rx buffer overflow\n\nThe MCTP serial receive state machine reads a frame length byte in\nmctp_serial_push_header() case 2 and validates it upper-bound-only:\n\n\tif (c \u003e MCTP_SERIAL_FRAME_MTU) {\n\t\tdev-\u003erxstate = STATE_ERR;\n\t} else {\n\t\tdev-\u003erxlen = c;\n\t\tdev-\u003erxpos = 0;\n\t\tdev-\u003erxstate = STATE_DATA;\n\t\t...\n\t}\n\nA length of zero passes this check, so rxlen is set to 0 and the state\nmachine advances to STATE_DATA. In mctp_serial_push() STATE_DATA, the\nincoming byte is stored and rxpos incremented before the terminator is\n\n\tdev-\u003erxbuf[dev-\u003erxpos] = c;\n\tdev-\u003erxpos++;\n\tdev-\u003erxstate = STATE_DATA;\n\tif (dev-\u003erxpos == dev-\u003erxlen) {\n\t\tdev-\u003erxpos = 0;\n\t\tdev-\u003erxstate = STATE_TRAILER;\n\t}\n\nWith rxlen == 0 the \"rxpos == rxlen\" terminator can never fire (rxpos is\nalready 1 on the first data byte), so subsequent bytes are written past\nthe end of the fixed 74-byte rxbuf, which is the last member of the\nnetdev private area. Every following data byte is an attacker-controlled\n1-byte out-of-bounds heap write, and the overflow continues until a\nframe (0x7e) or escape byte resets the parser -- effectively unbounded.\n\nReaching this requires CAP_NET_ADMIN to attach the N_MCTP line\ndiscipline and bring the resulting mctpserialN netdev up, after which\nthe bytes arrive via the tty receive path.\n\nRoute a zero-length frame straight to STATE_TRAILER instead of\nSTATE_DATA. The trailer/framing bytes are still consumed, and the frame\nresolves to a zero-length skb that the MCTP core rejects; the parser\nnever enters STATE_DATA with rxlen == 0, so the out-of-bounds write can\nno longer occur.\n\nKASAN, on a frame of 0x7e 0x01 0x00 followed by data bytes (before this\nchange):\n\n UBSAN: array-index-out-of-bounds in drivers/net/mctp/mctp-serial.c:370\n index 74 is out of range for type \u0027u8 [74]\u0027\n BUG: KASAN: slab-out-of-bounds in mctp_serial_tty_receive_buf\n Write of size 1 at addr ... by task kworker/u16:0\n mctp_serial_tty_receive_buf\n tty_ldisc_receive_buf\n flush_to_ldisc\n Allocated by task 152:\n alloc_netdev_mqs\n mctp_serial_open\n\nv2: route zero-length frames to STATE_TRAILER instead of STATE_ERR so\n the trailer/framing bytes are still consumed (Jeremy Kerr).\n\nFound by 0sec automated security-research tooling (https://0sec.ai)."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 9.6,
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:A - The bug is triggered in mctp_serial_tty_receive_buf() by crafted DSP0253 serial frames; on BMC/datacenter systems MCTP-over-serial links management controllers on a shared management LAN, letting an adjacent unauthenticated peer inject 0x7e/0x01/0x00 frames without using host syscalls.\nAC:L - Exploitation is deterministic: a zero-length length byte bypasses the upper-bound check, then each following serial byte is a controlled 1-byte heap OOB write until 0x7e/0x7d resets the parser; no races or attacker-uncontrollable memory layout are required.\nPR:N - Triggering the overflow only requires delivering malicious serial bytes to an already-configured, running mctpserial netdev; a remote/adjacent MCTP peer or compromised management controller needs no Linux host credentials, CAP_NET_ADMIN, or root on the victim.\nUI:N - No victim user action is required at exploit time; administrative enablement of MCTP serial is deployment configuration, not end-user interaction under CVSS.\nS:C - Kconfig documents virtio-serial VM interconnect for MCTP serial; a malicious guest sending crafted frames to the host-side mctpserial binding can corrupt host kernel heap memory, crossing the guest/host virtualization security boundary.\nC:H - Each overflow byte is attacker-controlled and the write stream is effectively unbounded past the 74-byte rxbuf (last netdev private field), enabling slab-out-of-bounds corruption that can be leveraged for arbitrary kernel memory disclosure.\nI:H - Sustained attacker-controlled out-of-bounds heap writes can corrupt adjacent kmalloc objects, function pointers, and netdev state, providing a standard path to arbitrary kernel write and privilege-escalating code execution.\nA:H - KASAN/UBSAN report slab-out-of-bounds and array-index-out-of-bounds in mctp_serial_tty_receive_buf via flush_to_ldisc; continued overflow reliably causes kernel oops/panic or hang during tty receive processing."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-19T16:29:36.851Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/64b96ae7912244d55257aa330d9569ee0a8f8d99"
},
{
"url": "https://git.kernel.org/stable/c/36dc6d6964a3b90411cc7944cd9b8b6f67b9807b"
},
{
"url": "https://git.kernel.org/stable/c/68819427bc07eca7963a9e8be19e5272cc29186c"
},
{
"url": "https://git.kernel.org/stable/c/f80ba170d7b3a44e3d244a2c8e06031d61bf3b23"
},
{
"url": "https://git.kernel.org/stable/c/06a6b606129c8a25cd457760f5370f3ff01fe05d"
},
{
"url": "https://git.kernel.org/stable/c/793b9b729f1e8de57be8c8daf1a9838be96cabed"
}
],
"title": "mctp: serial: handle zero-length frames to prevent rx buffer overflow",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-68124",
"datePublished": "2026-08-10T11:58:44.997Z",
"dateReserved": "2026-07-30T09:28:09.369Z",
"dateUpdated": "2026-08-19T16:29:36.851Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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