CVE-2026-68136 (GCVE-0-2026-68136)
Vulnerability from cvelistv5
Published
2026-08-10 11:58
Modified
2026-08-23 12:45
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
net: gro: fix double aggregation of flush-marked skbs
Commit 0ab03f353d36 ("net-gro: Fix GRO flush when receiving a GSO
packet.") added a flush check to skb_gro_receive(), but
skb_gro_receive_list() lacks the same validation.
As a result, packets marked with NAPI_GRO_CB(skb)->flush may still be
re-aggregated.
This allows already-GRO'd packets with existing frag_list to be
re-aggregated into a new GRO session, corrupting the frag_list chain
structure. When skb_segment() attempts to unpack these malformed packets,
it encounters invalid state and triggers a kernel panic.
Scenario (Tethering/Device forwarding):
1. Driver: Generated aggregated packet P1 via LRO with frag_list
2. Dev A: Receives aggregated fraglist packet and flush flag set
3. Dev A: Re-enters GRO, skb_gro_receive_list() is called
4. Missing flush check allows re-aggregation despite flush flag
5. Frag_list chain becomes corrupted (loops or dangling refs)
6. Dev B: TX path calls skb_segment(), crashes on corrupted frag_list
Root cause in skb_segment():
The check at line ~4891:
if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) &&
(skb_headlen(list_skb) == len || sg)) {
When frag_list is corrupted by double aggregation, when list_skb is
a NULL pointer from skb->next, skb_headlen(list_skb) dereference
NULL/corrupted pointers occurs.
Call Trace:
skb_headlen(NULL skb)
skb_segment
tcp_gso_segment
tcp4_gso_segment
inet_gso_segment
skb_mac_gso_segment
__skb_gso_segment
skb_gso_segment
validate_xmit_skb
validate_xmit_skb_list
sch_direct_xmit
qdisc_restart
__qdisc_run
qdisc_run
net_tx_action
Fix: Add NAPI_GRO_CB(skb)->flush validation to the early-return check in
skb_gro_receive_list(), matching the defensive programming pattern of
skb_gro_receive().
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 Version: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 |
||
{
"containers": {
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{
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"product": "Linux",
"programFiles": [
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{
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{
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{
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"versionType": "original_commit_for_fix"
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}
],
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gro: fix double aggregation of flush-marked skbs\n\nCommit 0ab03f353d36 (\"net-gro: Fix GRO flush when receiving a GSO\npacket.\") added a flush check to skb_gro_receive(), but\nskb_gro_receive_list() lacks the same validation.\n\nAs a result, packets marked with NAPI_GRO_CB(skb)-\u003eflush may still be\nre-aggregated.\n\nThis allows already-GRO\u0027d packets with existing frag_list to be\nre-aggregated into a new GRO session, corrupting the frag_list chain\nstructure. When skb_segment() attempts to unpack these malformed packets,\nit encounters invalid state and triggers a kernel panic.\n\nScenario (Tethering/Device forwarding):\n 1. Driver: Generated aggregated packet P1 via LRO with frag_list\n 2. Dev A: Receives aggregated fraglist packet and flush flag set\n 3. Dev A: Re-enters GRO, skb_gro_receive_list() is called\n 4. Missing flush check allows re-aggregation despite flush flag\n 5. Frag_list chain becomes corrupted (loops or dangling refs)\n 6. Dev B: TX path calls skb_segment(), crashes on corrupted frag_list\n\nRoot cause in skb_segment():\n The check at line ~4891:\n if (hsize \u003c= 0 \u0026\u0026 i \u003e= nfrags \u0026\u0026 skb_headlen(list_skb) \u0026\u0026\n (skb_headlen(list_skb) == len || sg)) {\n\n When frag_list is corrupted by double aggregation, when list_skb is\n a NULL pointer from skb-\u003enext, skb_headlen(list_skb) dereference\n NULL/corrupted pointers occurs.\n\nCall Trace:\n skb_headlen(NULL skb)\n skb_segment\n tcp_gso_segment\n tcp4_gso_segment\n inet_gso_segment\n skb_mac_gso_segment\n __skb_gso_segment\n skb_gso_segment\n validate_xmit_skb\n validate_xmit_skb_list\n sch_direct_xmit\n qdisc_restart\n __qdisc_run\n qdisc_run\n net_tx_action\n\nFix: Add NAPI_GRO_CB(skb)-\u003eflush validation to the early-return check in\nskb_gro_receive_list(), matching the defensive programming pattern of\nskb_gro_receive()."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - The bug is reached from the standard NAPI GRO receive path processing remotely originated TCP/IP packets (napi_gro_receive\u2192dev_gro_receive\u2192tcp_gro_receive\u2192skb_gro_receive_list), including tethering/NAT/forwarding scenarios where packets re-enter GRO on a second netdev after driver LRO or prior GRO aggregation.\nAC:L - An attacker can reliably trigger the bug by crafting a TCP stream through a forwarding host with rx-gro-list enabled, without races or victim-specific timing; the commit documents a deterministic tethering/forwarding repro where flush-marked frag_list skbs are re-aggregated and later crash skb_segment.\nPR:N - No local privileges or authentication are required; any remote peer that can send TCP traffic through a vulnerable forwarding/tethering/NAT Linux host can reach the GRO fraglist merge path, which performs no capability or credential checks on the receive path.\nUI:N - Exploitation requires only network-delivered packets and normal kernel forwarding/GRO processing; the victim does not need to open files, mount filesystems, click links, or perform any deliberate action beyond routine network operation.\nS:U - Impact is confined to kernel memory corruption and panic within the same host kernel security domain during packet GRO aggregation and subsequent segmentation on transmit; it does not cross VM, container, or IOMMU boundaries to affect a separate security authority.\nC:H - Double aggregation corrupts the skb frag_list chain (loops, dangling references, NULL/corrupted list_skb pointers), constituting kernel heap memory corruption that can be read during skb_segment processing and is classifiable as a high-impact info-disclosure primitive beyond a simple crash.\nI:H - Re-aggregating flush-marked skbs with existing frag_list corrupts skb linked-list structure and reference relationships in kernel memory, enabling potential control of subsequent skb metadata and write/control-flow primitives during GSO segmentation, not merely integrity-preserving packet drops.\nA:H - Corrupted frag_list state causes skb_segment to dereference a NULL or invalid list_skb via skb_headlen(), producing a kernel panic/oops on the transmit path (sch_direct_xmit/qdisc_run), fully denying availability of the affected system."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-23T12:45:54.689Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/7fc7e35212cf58c134310fb47566a844297ceae9"
},
{
"url": "https://git.kernel.org/stable/c/d1fb23f8f794ac4683127bd49a6422bd87e0ac02"
},
{
"url": "https://git.kernel.org/stable/c/db3e82da616f52e2b27e25e7be3fde2f2a5e54d6"
},
{
"url": "https://git.kernel.org/stable/c/107e1a469f53a2a70874f3f12bf6fcd23925da1d"
},
{
"url": "https://git.kernel.org/stable/c/a4dfd46cc8f08a29c6183794790547d0945f3d45"
},
{
"url": "https://git.kernel.org/stable/c/fc0c0f7a207f0cd2d2aa725696c907f7d03af9e0"
},
{
"url": "https://git.kernel.org/stable/c/e751256486d0ded20f5a9f9863467f1dce65142f"
}
],
"title": "net: gro: fix double aggregation of flush-marked skbs",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-68136",
"datePublished": "2026-08-10T11:58:59.450Z",
"dateReserved": "2026-07-30T09:28:09.370Z",
"dateUpdated": "2026-08-23T12:45:54.689Z",
"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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