CVE-2026-98954 (GCVE-0-2026-98954)
Vulnerability from cvelistv5
Published
2026-10-23 12:19
Modified
2026-10-23 12:19
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
net: always dissect GSO packets in __virtio_net_hdr_to_skb()
Commit 9e8db5913264 ("net: avoid false positives in untrusted gso
validation") added a '&& skb->network_header' check before flow-dissecting
GSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM in
__virtio_net_hdr_to_skb(), because some callers (such as tun_get_user(),
tun_xdp_one(), virtnet_receive_done(), and raw_verify_header()) called
virtio_net_hdr_*_to_skb() before initializing skb->network_header and
skb->dev.
Because __alloc_skb() and __build_skb_around() zero-initialize
skb->network_header to 0 (unlike mac_header and transport_header which
are initialized to ~0U), those four callers always had
skb->network_header == 0 and bypassed flow dissection in
__virtio_net_hdr_to_skb(). More generally, skb->network_header is an
offset from skb->head (where 0 is also a valid offset whenever
skb_headroom(skb) is 0), not a boolean flag.
Whenever the 'if (gso_type && skb->network_header)' branch was skipped,
the fallback 'else if (gso_type)' only pulled nh_min_len + thlen (40 bytes
for TCPv4) without dissecting the packet, without validating ip_proto or
n_proto, and without setting skb->transport_header.
If the packet has a malformed network header, it is not rejected and a
subsequent skb_probe_transport_header() also fails, leaving
skb->transport_header at ~0U (0xffff). Similarly, if an IPv4 packet
carries IP options (ihl > 5) or an IPv6 packet carries extension headers,
pulling only nh_min_len + thlen can leave the TCP header outside
skb->head. In both cases, tcp_hdrlen(skb) in skb_gso_transport_seglen()
reads out-of-bounds:
BUG: KASAN: slab-out-of-bounds in skb_gso_transport_seglen
Read of size 2 by task poc/133
skb_gso_transport_seglen (net/core/gso.c:155)
skb_gso_validate_mac_len (net/core/gso.c:270)
tbf_enqueue (net/sched/sch_tbf.c:260)
dev_qdisc_enqueue (net/core/dev.c:4227)
__dev_queue_xmit (net/core/dev.c:4884)
In addition, checking virtio_net_hdr_match_proto() only inside
'if (!skb->protocol)' before flow dissection both skipped validation when
skb->protocol was pre-set by the caller and rejected VLAN-tagged frames
whose outer L2 protocol is ETH_P_8021Q or ETH_P_8021AD.
Fix this by:
1. Initializing skb->dev and skb->network_header (plus skb->protocol for
IFF_TUN) before virtio_net_hdr_*_to_skb() in tun_get_user(),
tun_xdp_one(), virtnet_receive_done(), and raw_verify_header(). In
tun_get_user(), drop the redundant skb_reset_mac_header(skb) in the
IFF_TUN case since __virtio_net_hdr_to_skb() unconditionally resets
mac_header.
2. Removing '&& skb->network_header' and the unvalidated
'else if (gso_type)' fallback in __virtio_net_hdr_to_skb() so all GSO
packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are flow-dissected, have
their transport header pulled into linear data, and have
skb->transport_header set.
3. Moving the virtio_net_hdr_match_proto() check to after
skb_flow_dissect_flow_keys_basic(), validating keys.basic.n_proto
against hdr_gso_type.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: d5be7f632bad0f489879eed0ff4b99bd7fe0b74c Version: d5be7f632bad0f489879eed0ff4b99bd7fe0b74c Version: dac7d4432b13d6b58923c1178b786bcda37c9e9e Version: e93384b12443c9bb6830b56b7d299beed432b865 Version: f709f7b28d76de327373598a0fda9f916c36b5e6 Version: d996573ebd5c528c613e90b7e7daa961d58fa16e Version: c375152be9dd9d6fbf6ae5ac8be337d0590f192a Version: 0dab7eb86ea06ce8c530785f1999948c6f223c96 Version: ea3fb2ce5fa794d02135f5c079e05cd6fc3f545d Version: 54ef8243c3c8e90f1ea5792e6752e021a25c8eb3 Version: 4.14.104 ≤ Version: 4.19.26 ≤ Version: 4.20.13 ≤ Version: 4.14.226 ≤ Version: 4.19.181 ≤ |
||
{
"containers": {
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"programFiles": [
"arch/um/drivers/vector_transports.c",
"drivers/net/tun.c",
"drivers/net/virtio_net.c",
"include/linux/virtio_net.h"
],
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"status": "affected",
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]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"arch/um/drivers/vector_transports.c",
"drivers/net/tun.c",
"drivers/net/virtio_net.c",
"include/linux/virtio_net.h"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "5.0"
},
{
"lessThan": "5.0",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.2.*",
"status": "unaffected",
"version": "7.2.11",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
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},
{
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],
"negate": false,
"operator": "OR"
}
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],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: always dissect GSO packets in __virtio_net_hdr_to_skb()\n\nCommit 9e8db5913264 (\"net: avoid false positives in untrusted gso\nvalidation\") added a \u0027\u0026\u0026 skb-\u003enetwork_header\u0027 check before flow-dissecting\nGSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM in\n__virtio_net_hdr_to_skb(), because some callers (such as tun_get_user(),\ntun_xdp_one(), virtnet_receive_done(), and raw_verify_header()) called\nvirtio_net_hdr_*_to_skb() before initializing skb-\u003enetwork_header and\nskb-\u003edev.\n\nBecause __alloc_skb() and __build_skb_around() zero-initialize\nskb-\u003enetwork_header to 0 (unlike mac_header and transport_header which\nare initialized to ~0U), those four callers always had\nskb-\u003enetwork_header == 0 and bypassed flow dissection in\n__virtio_net_hdr_to_skb(). More generally, skb-\u003enetwork_header is an\noffset from skb-\u003ehead (where 0 is also a valid offset whenever\nskb_headroom(skb) is 0), not a boolean flag.\n\nWhenever the \u0027if (gso_type \u0026\u0026 skb-\u003enetwork_header)\u0027 branch was skipped,\nthe fallback \u0027else if (gso_type)\u0027 only pulled nh_min_len + thlen (40 bytes\nfor TCPv4) without dissecting the packet, without validating ip_proto or\nn_proto, and without setting skb-\u003etransport_header.\n\nIf the packet has a malformed network header, it is not rejected and a\nsubsequent skb_probe_transport_header() also fails, leaving\nskb-\u003etransport_header at ~0U (0xffff). Similarly, if an IPv4 packet\ncarries IP options (ihl \u003e 5) or an IPv6 packet carries extension headers,\npulling only nh_min_len + thlen can leave the TCP header outside\nskb-\u003ehead. In both cases, tcp_hdrlen(skb) in skb_gso_transport_seglen()\nreads out-of-bounds:\n\n BUG: KASAN: slab-out-of-bounds in skb_gso_transport_seglen\n Read of size 2 by task poc/133\n skb_gso_transport_seglen (net/core/gso.c:155)\n skb_gso_validate_mac_len (net/core/gso.c:270)\n tbf_enqueue (net/sched/sch_tbf.c:260)\n dev_qdisc_enqueue (net/core/dev.c:4227)\n __dev_queue_xmit (net/core/dev.c:4884)\n\nIn addition, checking virtio_net_hdr_match_proto() only inside\n\u0027if (!skb-\u003eprotocol)\u0027 before flow dissection both skipped validation when\nskb-\u003eprotocol was pre-set by the caller and rejected VLAN-tagged frames\nwhose outer L2 protocol is ETH_P_8021Q or ETH_P_8021AD.\n\nFix this by:\n1. Initializing skb-\u003edev and skb-\u003enetwork_header (plus skb-\u003eprotocol for\n IFF_TUN) before virtio_net_hdr_*_to_skb() in tun_get_user(),\n tun_xdp_one(), virtnet_receive_done(), and raw_verify_header(). In\n tun_get_user(), drop the redundant skb_reset_mac_header(skb) in the\n IFF_TUN case since __virtio_net_hdr_to_skb() unconditionally resets\n mac_header.\n2. Removing \u0027\u0026\u0026 skb-\u003enetwork_header\u0027 and the unvalidated\n \u0027else if (gso_type)\u0027 fallback in __virtio_net_hdr_to_skb() so all GSO\n packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are flow-dissected, have\n their transport header pulled into linear data, and have\n skb-\u003etransport_header set.\n3. Moving the virtio_net_hdr_match_proto() check to after\n skb_flow_dissect_flow_keys_basic(), validating keys.basic.n_proto\n against hdr_gso_type."
}
],
"providerMetadata": {
"dateUpdated": "2026-10-23T12:19:13.873Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c"
},
{
"url": "https://git.kernel.org/stable/c/44378d02c5aaae24b60a75fbbb539b4aa4db503d"
}
],
"title": "net: always dissect GSO packets in __virtio_net_hdr_to_skb()",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-98954",
"datePublished": "2026-10-23T12:19:13.873Z",
"dateReserved": "2026-09-25T10:25:14.382Z",
"dateUpdated": "2026-10-23T12:19:13.873Z",
"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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