{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-80976", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-80976" ], "published": "2026-09-11T19:47:07Z", "summary": "seg6: reset IP6CB after IPv6 decapsulation", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nseg6: reset IP6CB after IPv6 decapsulation\n\ndecap_and_validate() pulls the outer SRv6 headers and makes the inner\npacket the skb network header. The IPv6 control block still contains\nvalues collected while parsing the outer packet, including nhoff and\nextension-header flags.\n\nEnd.DX6 and End.DT6 route the inner IPv6 packet directly to the IPv6\ninput path. An unprivileged user can reach End.DT6 from a user and net\nnamespace by installing a local SID and injecting an outer packet with\nHop-by-Hop and Destination Options headers followed by an SRH and a\nminimal inner IPv6 packet.\n\nThe outer extension headers leave a large nhoff in IP6CB. After\ndecapsulation, ip6_protocol_deliver_rcu() uses that stale offset on the\ninner packet and reads beyond the skb head. KASAN reports:\n\n BUG: KASAN: slab-out-of-bounds in ip6_protocol_deliver_rcu\n ip6_protocol_deliver_rcu+0x1118/0x1450\n ip6_input_finish+0x11b/0x240\n seg6_local_input_core+0xed/0x2e0\n lwtunnel_input+0x1e9/0x4e0\n ipv6_rthdr_rcv+0x525f/0x6c50\n ip6_protocol_deliver_rcu+0xcb7/0x1450\n\nBefore clearing IP6CB for an inner IPv6 packet, save its incoming\ninterface index and L3 slave state. Restore both after the clear and set\nnhoff to the inner IPv6 base-header nexthdr field.\n\nUse IP6CB(skb)->iif rather than skb->skb_iif because VRF processing can\nreplace skb_iif with the L3 master while IP6CB keeps the receiving\ninterface. Preserve IP6SKB_L3SLAVE for the same reason.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.188", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-80976" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/d1f0d353358987ca87f21d8956e2d2854951130d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/a0e2b0a3718f0cf9fb0ee41710b4a6348a7315c8" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/9ae92198c24d7dacd4070e2f34f6e1ed3a63061c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/96c74420ac92930a7e0f21770818544eee4a93d7" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/2b154e96fcb3f01fd42765c64e0a56820fbc16eb" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/cfa186a0857a0f831dfca67b16bbc40ecfdf3280" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/c73fb911e02b9a766c950bc9707f3e3a96ffd702" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f967455fb2a5a2079b9eb5823e9ccf359174bf9f" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-09-14T12:06:03Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 9.8, "cvss_v3_severity": "Critical", "scenario": "AV:N - End.DT6/End.DX6 run on the IPv6 receive path (ipv6_rthdr_rcv/lwtunnel_input/seg6_local_input_core) when a packet targets a configured local SID; a remote attacker who can route IPv6/SRv6 traffic to that SID on an SRv6 PE, VPN edge, or similar node triggers decap without local access.\nAC:L - The attacker fully controls the outer Hop-by-Hop and Destination Options chain that inflates IP6CB nhoff and the inner packet length, so one crafted packet deterministically makes ip6_protocol_deliver_rcu() index past the skb head with no race or uncontrolled layout.\nPR:N - SID processing runs in receive softirq with no authentication; a configured End.DT6/End.DX6 SID is an environmental precondition, not a credential the network attacker must hold (the same path is also reachable by an unprivileged userns user installing a SID).\nUI:N - Exploitation requires only sending crafted IPv6 packets to the SID; no victim user or administrator action is needed beyond the pre-existing SRv6 configuration.\nS:U - The stale-nhoff out-of-bounds access affects kernel memory on the receiving host only; it does not cross a VM, IOMMU, or sandbox security boundary.\nC:H - After decap, ip6_protocol_deliver_rcu() does skb_network_header(skb)[nhoff] using a stale outer nhoff the attacker can push thousands of bytes past the inner skb, which is an out-of-bounds kernel read; the leaked byte is then used as nexthdr, exposing further slab contents via dispatch side effects.\nI:H - Stale nhoff selects the inet6 protocol handler, type-confusing the inner packet into an attacker-influenced parser; IPv6 fragment reassembly also writes skb_network_header(skb)[nhoff], so the same attacker-controlled offset becomes an out-of-bounds write when the inner flow is fragmented.\nA:H - KASAN reports slab-out-of-bounds in ip6_protocol_deliver_rcu() on this path; in production a large nhoff lands on unmapped memory and oopses/panics the kernel, and the packet can be repeated at line rate." } } }