{"id":"CVE-2026-80590","state":"PUBLISHED","title":"inet: frags: strip GSO state from fragments before reassembly","description":"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's skb as the head of the reassembled datagram, including its\nshinfo->gso_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()'s 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   <TASK>\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   </TASK>\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 >= nfrags) and BUG_ON(!list_skb->head_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.","publishedAt":"2026-08-28T06:35:12.516Z","updatedAt":"2026-10-19T08:43:12.426Z","severity":{"score":8.6,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"cfdbc8c2e6f9ef5d8b8e54859da03dfe682b0bee","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"29dda278a5ed272f2230ff4eaa23cf403107bba0","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"14a8f3e10fa9a5abd6cedcdaa0c0b7ea9a09f234","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"3edf721bb4b99d272c336631b44e3d8ff9a4f31b","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"dec2edb7aaf12a8878b3a03172ea8fc277b8eaad","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"c49f04e8d2b94dbb8d9fd99731dd3f00589c8ace","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"69b73b74d9eb45f5560a8fe4fa406ada580e1340","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"da857e448322a2e871ce3ecc2900027041160d43","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"d5dc1e69fd7258ea605c9952e5d5947539159ae3","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/inet_fragment.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.27","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.27","versionType":"semver"},{"version":"5.10.268","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.219","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.186","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.155","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.107","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.48","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.12","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2.2","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/inet_fragment.c"]}],"references":["https://git.kernel.org/stable/c/cfdbc8c2e6f9ef5d8b8e54859da03dfe682b0bee","https://git.kernel.org/stable/c/29dda278a5ed272f2230ff4eaa23cf403107bba0","https://git.kernel.org/stable/c/14a8f3e10fa9a5abd6cedcdaa0c0b7ea9a09f234","https://git.kernel.org/stable/c/3edf721bb4b99d272c336631b44e3d8ff9a4f31b","https://git.kernel.org/stable/c/dec2edb7aaf12a8878b3a03172ea8fc277b8eaad","https://git.kernel.org/stable/c/c49f04e8d2b94dbb8d9fd99731dd3f00589c8ace","https://git.kernel.org/stable/c/69b73b74d9eb45f5560a8fe4fa406ada580e1340","https://git.kernel.org/stable/c/da857e448322a2e871ce3ecc2900027041160d43","https://git.kernel.org/stable/c/d5dc1e69fd7258ea605c9952e5d5947539159ae3"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:07.220Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/80xxx/CVE-2026-80590.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-80590","state":"PUBLISHED","datePublished":"2026-08-28T06:35:12.516Z","dateUpdated":"2026-10-19T08:43:12.426Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-26T14:34:25.770Z"},"containers":{"cna":{"title":"inet: frags: strip GSO state from fragments before reassembly","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's skb as the head of the reassembled datagram, including its\nshinfo->gso_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()'s 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   <TASK>\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   </TASK>\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 >= nfrags) and BUG_ON(!list_skb->head_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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"cfdbc8c2e6f9ef5d8b8e54859da03dfe682b0bee","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"29dda278a5ed272f2230ff4eaa23cf403107bba0","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"14a8f3e10fa9a5abd6cedcdaa0c0b7ea9a09f234","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"3edf721bb4b99d272c336631b44e3d8ff9a4f31b","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"dec2edb7aaf12a8878b3a03172ea8fc277b8eaad","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"c49f04e8d2b94dbb8d9fd99731dd3f00589c8ace","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"69b73b74d9eb45f5560a8fe4fa406ada580e1340","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"da857e448322a2e871ce3ecc2900027041160d43","versionType":"git"},{"version":"f43798c27684ab925adde7d8acc34c78c6e50df8","status":"affected","lessThan":"d5dc1e69fd7258ea605c9952e5d5947539159ae3","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/inet_fragment.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.27","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.27","versionType":"semver"},{"version":"5.10.268","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.219","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.186","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.155","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.107","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.48","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.12","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2.2","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/inet_fragment.c"]}],"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"},{"url":"https://git.kernel.org/stable/c/d5dc1e69fd7258ea605c9952e5d5947539159ae3"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","baseScore":8.6,"baseSeverity":"HIGH"},"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":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:43:12.426Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"5.10.268"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"5.15.219"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"6.1.186"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"6.6.155"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"6.12.107"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"6.18.48"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"7.1.12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"7.2.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.27","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-80590","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T19:18:13.413771Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:29.280Z"}}]}}}