CVE-2026-80590 (GCVE-0-2026-80590)
Vulnerability from cvelistv5
Published
2026-08-28 06:35
Modified
2026-08-29 06:21
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
inet: frags: strip GSO state from fragments before reassembly
A virtio_net_hdr (tun/tap, or AF_PACKET with PACKET_VNET_HDR) can mark
an IPv4 or IPv6 fragment as GSO; nothing relates gso_type to frag_off.
inet_frag_reasm_prepare()/inet_frag_reasm_finish() keep the first
fragment's skb as the head of the reassembled datagram, including its
shinfo->gso_size/gso_type/gso_segs, and chain the remaining fragments
on frag_list with whatever linear/paged layout they arrived with.
After ip_defrag() (ip_local_deliver(), nf_defrag_ipv4, ...) the
reassembled skb therefore still claims to be GSO (SKB_GSO_DODGY), and
the next software segmentation point - udp_rcv_segment() on local
delivery, validate_xmit_skb(), or the ip_finish_output_gso() slow
path - hands it to skb_segment(). skb_segment()'s frag_list walk
assumes GRO-shaped input and hits one of its BUG_ON()s. Two writes to
a tap by an unprivileged user in its own userns are enough:
kernel BUG at net/core/skbuff.c:4899!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 1000 PID: 82 Comm: poc Not tainted 7.2.0-pentest+ #2
RIP: 0010:skb_segment+0x20ca/0x48b0
Call Trace:
<TASK>
__udp_gso_segment+0x29a/0x27d0
udp4_ufo_fragment+0x458/0x6c0
inet_gso_segment+0x429/0x1340
skb_mac_gso_segment+0x233/0x4f0
__skb_gso_segment+0x308/0x660
udp_queue_rcv_skb+0x440/0xad0
udp_unicast_rcv_skb+0xc7/0x2c0
udp_rcv+0x16ce/0x2260
ip_protocol_deliver_rcu+0x197/0x2d0
ip_local_deliver+0x430/0x690
ip_rcv+0x16f/0x1f0
__netif_receive_skb_one_core+0x15e/0x1c0
__netif_receive_skb+0x1e/0x110
netif_receive_skb+0xf6/0x5c0
tun_rx_batched.isra.0+0x3ab/0x790
tun_get_user+0x17c3/0x3550
tun_chr_write_iter+0xba/0x1b0
vfs_write+0x646/0x1130
</TASK>
Kernel panic - not syncing: Fatal exception in interrupt
This runs with BH disabled, so it is a panic rather than an oops. The
same is reachable with CAP_NET_RAW in a netns where a defrag point
precedes a GSO point, and from a guest whose VMM forwards
virtio_net_hdr to a tap. The SKB_GSO_DODGY frag_list checks added by
commit 3dcbdb134f32 ("net: gso: Fix skb_segment splat when splitting
gso_size mangled skb having linear-headed frag_list") and by
commit 9e4b7a99a03a ("net: gso: fix panic on frag_list with mixed head
alloc types") do not cover it: page-backed heads skip them, and kmalloc
heads skip them when gso_size == skb_headlen(head), which the sender
controls.
An skb entering a frag queue is an IP fragment by definition and
cannot legitimately carry GSO state: GRO does not merge fragments and
the stack segments before it fragments, so only untrusted sources are
affected. This has been reachable since
commit f43798c27684 ("tun: Allow GSO using virtio_net_hdr"), the first
path that let userspace attach GSO metadata to an IP fragment. Reset
the GSO fields of every fragment as it is queued, in
inet_frag_queue_insert(), which IPv4, IPv6, nf_conntrack_reasm and
6lowpan reassembly share; then neither the head nor the frag_list
members of the reassembled skb carry them (the members matter too:
the ip_do_fragment()/ip6_fragment() fast paths send them out as they
are). The head may remain CHECKSUM_PARTIAL; that is already accepted
on receive and resolved by skb_checksum_help() in
ip_do_fragment()/ip6_fragment() on forward.
Tested on top of net.git (dc4b95b8fee9), x86_64: the tap reproducer
above, two further IPv4 frag_list geometries that reach
BUG_ON(i >= nfrags) and BUG_ON(!list_skb->head_frag), and an IPv6
fragment-header variant (udp6_ufo_fragment()) each panic the unpatched
kernel; with this patch all four datagrams are delivered intact and
nothing is logged.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 Version: f43798c27684ab925adde7d8acc34c78c6e50df8 |
||
{
"containers": {
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}
],
"cpeApplicability": [
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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\ninet: frags: strip GSO state from fragments before reassembly\n\nA virtio_net_hdr (tun/tap, or AF_PACKET with PACKET_VNET_HDR) can mark\nan IPv4 or IPv6 fragment as GSO; nothing relates gso_type to frag_off.\ninet_frag_reasm_prepare()/inet_frag_reasm_finish() keep the first\nfragment\u0027s skb as the head of the reassembled datagram, including its\nshinfo-\u003egso_size/gso_type/gso_segs, and chain the remaining fragments\non frag_list with whatever linear/paged layout they arrived with.\n\nAfter ip_defrag() (ip_local_deliver(), nf_defrag_ipv4, ...) the\nreassembled skb therefore still claims to be GSO (SKB_GSO_DODGY), and\nthe next software segmentation point - udp_rcv_segment() on local\ndelivery, validate_xmit_skb(), or the ip_finish_output_gso() slow\npath - hands it to skb_segment(). skb_segment()\u0027s frag_list walk\nassumes GRO-shaped input and hits one of its BUG_ON()s. Two writes to\na tap by an unprivileged user in its own userns are enough:\n\n kernel BUG at net/core/skbuff.c:4899!\n Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI\n CPU: 0 UID: 1000 PID: 82 Comm: poc Not tainted 7.2.0-pentest+ #2\n RIP: 0010:skb_segment+0x20ca/0x48b0\n Call Trace:\n \u003cTASK\u003e\n __udp_gso_segment+0x29a/0x27d0\n udp4_ufo_fragment+0x458/0x6c0\n inet_gso_segment+0x429/0x1340\n skb_mac_gso_segment+0x233/0x4f0\n __skb_gso_segment+0x308/0x660\n udp_queue_rcv_skb+0x440/0xad0\n udp_unicast_rcv_skb+0xc7/0x2c0\n udp_rcv+0x16ce/0x2260\n ip_protocol_deliver_rcu+0x197/0x2d0\n ip_local_deliver+0x430/0x690\n ip_rcv+0x16f/0x1f0\n __netif_receive_skb_one_core+0x15e/0x1c0\n __netif_receive_skb+0x1e/0x110\n netif_receive_skb+0xf6/0x5c0\n tun_rx_batched.isra.0+0x3ab/0x790\n tun_get_user+0x17c3/0x3550\n tun_chr_write_iter+0xba/0x1b0\n vfs_write+0x646/0x1130\n \u003c/TASK\u003e\n Kernel panic - not syncing: Fatal exception in interrupt\n\nThis runs with BH disabled, so it is a panic rather than an oops. The\nsame is reachable with CAP_NET_RAW in a netns where a defrag point\nprecedes a GSO point, and from a guest whose VMM forwards\nvirtio_net_hdr to a tap. The SKB_GSO_DODGY frag_list checks added by\ncommit 3dcbdb134f32 (\"net: gso: Fix skb_segment splat when splitting\ngso_size mangled skb having linear-headed frag_list\") and by\ncommit 9e4b7a99a03a (\"net: gso: fix panic on frag_list with mixed head\nalloc types\") do not cover it: page-backed heads skip them, and kmalloc\nheads skip them when gso_size == skb_headlen(head), which the sender\ncontrols.\n\nAn skb entering a frag queue is an IP fragment by definition and\ncannot legitimately carry GSO state: GRO does not merge fragments and\nthe stack segments before it fragments, so only untrusted sources are\naffected. This has been reachable since\ncommit f43798c27684 (\"tun: Allow GSO using virtio_net_hdr\"), the first\npath that let userspace attach GSO metadata to an IP fragment. Reset\nthe GSO fields of every fragment as it is queued, in\ninet_frag_queue_insert(), which IPv4, IPv6, nf_conntrack_reasm and\n6lowpan reassembly share; then neither the head nor the frag_list\nmembers of the reassembled skb carry them (the members matter too:\nthe ip_do_fragment()/ip6_fragment() fast paths send them out as they\nare). The head may remain CHECKSUM_PARTIAL; that is already accepted\non receive and resolved by skb_checksum_help() in\nip_do_fragment()/ip6_fragment() on forward.\n\nTested on top of net.git (dc4b95b8fee9), x86_64: the tap reproducer\nabove, two further IPv4 frag_list geometries that reach\nBUG_ON(i \u003e= nfrags) and BUG_ON(!list_skb-\u003ehead_frag), and an IPv6\nfragment-header variant (udp6_ufo_fragment()) each panic the unpatched\nkernel; with this patch all four datagrams are delivered intact and\nnothing is logged."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 8.6,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - A malicious cloud VM guest injects virtio_net_hdr-marked IPv4/IPv6 fragments through virtio-net/vhost-tap into the host ip_rcv() path; the same inet_frag reassembly and skb_segment() crash also fires on validate_xmit_skb()/ip_finish_output_gso() when such skbs traverse forwarding.\nAC:L - The attacker fully controls virtio_net_hdr gso_type/gso_size and fragment geometry; the commit reproduces a host panic from two tap writes with no races, timing, or uncontrollable memory layout required.\nPR:N - On typical KVM/QEMU tap-backed virtio-net deployments a tenant VM needs no host account or capability; exploitation uses only the pre-provisioned virtual NIC, not init-namespace root or CAP_NET_ADMIN on the host.\nUI:N - Packet injection, ip_defrag reassembly, and GSO segmentation run automatically in softirq once crafted virtio fragments are sent; no victim mount, click, or other cooperative action is required.\nS:C - A guest VM tenant can panic the host kernel by crossing the hypervisor virtio/tap boundary, impacting resources outside the guest security authority even though the demonstrated primitive is denial of service rather than full escape.\nC:N - Impact is an intentional BUG_ON in skb_segment() frag_list handling; there is no demonstrated out-of-bounds read, use-after-free, or other information-disclosure primitive before the assertion aborts.\nI:N - The failure aborts in skb_segment() before any out-of-bounds write, page-desc conversion, or control-flow hijack; attacker-controlled metadata only reaches a defensive assertion, not a memory modification primitive.\nA:H - Triggering skb_segment() BUG_ON from tun_rx/tun_get_user runs with BH disabled and causes a fatal kernel panic, fully and repeatedly denying availability of the affected host until reboot."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-29T06:21:05.276Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/cfdbc8c2e6f9ef5d8b8e54859da03dfe682b0bee"
},
{
"url": "https://git.kernel.org/stable/c/29dda278a5ed272f2230ff4eaa23cf403107bba0"
},
{
"url": "https://git.kernel.org/stable/c/14a8f3e10fa9a5abd6cedcdaa0c0b7ea9a09f234"
},
{
"url": "https://git.kernel.org/stable/c/3edf721bb4b99d272c336631b44e3d8ff9a4f31b"
},
{
"url": "https://git.kernel.org/stable/c/dec2edb7aaf12a8878b3a03172ea8fc277b8eaad"
},
{
"url": "https://git.kernel.org/stable/c/c49f04e8d2b94dbb8d9fd99731dd3f00589c8ace"
},
{
"url": "https://git.kernel.org/stable/c/69b73b74d9eb45f5560a8fe4fa406ada580e1340"
},
{
"url": "https://git.kernel.org/stable/c/da857e448322a2e871ce3ecc2900027041160d43"
}
],
"title": "inet: frags: strip GSO state from fragments before reassembly",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-80590",
"datePublished": "2026-08-28T06:35:12.516Z",
"dateReserved": "2026-08-26T14:34:25.770Z",
"dateUpdated": "2026-08-29T06:21:05.276Z",
"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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