{"id":"DEBIAN-CVE-2026-80590","details":"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-\u003egso_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:    \u003cTASK\u003e    __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    \u003c/TASK\u003e   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 \u003e= nfrags) and BUG_ON(!list_skb-\u003ehead_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.","modified":"2026-09-19T22:02:03.735643900Z","published":"2026-08-28T08:16:42.517Z","upstream":["CVE-2026-80590"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-80590"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.187-1"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.147-1","6.1.148-1","6.1.153-1","6.1.158-1","6.1.159-1","6.1.162-1","6.1.164-1","6.1.170-1","6.1.170-2","6.1.170-3","6.1.172-1","6.1.174-1","6.1.176-1","6.1.177-1","6.1.180-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1"],"ecosystem_specific":{"urgency":"not 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