{"id":"CVE-2026-80978","state":"PUBLISHED","title":"net: cap advertised IP tunnel headroom","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: cap advertised IP tunnel headroom\n\nIP tunnel devices derive their advertised needed_headroom from lower\noutput devices. A stack of user-created devices can make the derived\nvalue larger than the 16-bit skb header offsets can represent. Once IP\noutput reserves it, skb head expansion can wrap those offsets.\n\nThe runtime transmit path already caps a growing needed_headroom at 512.\nApply the same cap when tunnel configuration publishes needed_headroom\nderived from a lower output device.\n\nCapping the advertised value is safe: IP tunnel transmit still expands\nthe skb when a packet needs more headroom. A nonsensical stacked\nconfiguration can therefore incur an extra reallocation, but it cannot\npublish an unbounded reservation to upper layers.","publishedAt":"2026-09-11T19:42:39.496Z","updatedAt":"2026-10-19T08:46:02.787Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"fb889a619723032140f5d983a3a34d25a5a2bed4","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"b160422f8103574425e2834130e169d84c94fa1d","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"d36e75f5669140b66515ad3a176ca6337bd80a5e","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"84783961cb8bdb36b4f41a02ce43aafc6d52b176","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"bc4e05ae66c9797a0972ac44326e69c5305e0020","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"af0ee8f04bea22cdb331fa3509e17f81b48938ad","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"9144f2c53a04465a6878172b523f640313c5559e","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"6b222adeb9340306e2ff97127c76117abb9b3df8","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/ip_tunnels.h","net/ipv4/ip_tunnel.c","net/ipv6/ip6_gre.c","net/ipv6/ip6_tunnel.c","net/ipv6/sit.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.11","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","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":["include/net/ip_tunnels.h","net/ipv4/ip_tunnel.c","net/ipv6/ip6_gre.c","net/ipv6/ip6_tunnel.c","net/ipv6/sit.c"]}],"references":["https://git.kernel.org/stable/c/fb889a619723032140f5d983a3a34d25a5a2bed4","https://git.kernel.org/stable/c/b160422f8103574425e2834130e169d84c94fa1d","https://git.kernel.org/stable/c/d36e75f5669140b66515ad3a176ca6337bd80a5e","https://git.kernel.org/stable/c/84783961cb8bdb36b4f41a02ce43aafc6d52b176","https://git.kernel.org/stable/c/bc4e05ae66c9797a0972ac44326e69c5305e0020","https://git.kernel.org/stable/c/af0ee8f04bea22cdb331fa3509e17f81b48938ad","https://git.kernel.org/stable/c/9144f2c53a04465a6878172b523f640313c5559e","https://git.kernel.org/stable/c/6b222adeb9340306e2ff97127c76117abb9b3df8"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:07.220Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/80xxx/CVE-2026-80978.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-80978","state":"PUBLISHED","datePublished":"2026-09-11T19:42:39.496Z","dateUpdated":"2026-10-19T08:46:02.787Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-26T14:34:25.811Z"},"containers":{"cna":{"title":"net: cap advertised IP tunnel headroom","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: cap advertised IP tunnel headroom\n\nIP tunnel devices derive their advertised needed_headroom from lower\noutput devices. A stack of user-created devices can make the derived\nvalue larger than the 16-bit skb header offsets can represent. Once IP\noutput reserves it, skb head expansion can wrap those offsets.\n\nThe runtime transmit path already caps a growing needed_headroom at 512.\nApply the same cap when tunnel configuration publishes needed_headroom\nderived from a lower output device.\n\nCapping the advertised value is safe: IP tunnel transmit still expands\nthe skb when a packet needs more headroom. A nonsensical stacked\nconfiguration can therefore incur an extra reallocation, but it cannot\npublish an unbounded reservation to upper layers."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"fb889a619723032140f5d983a3a34d25a5a2bed4","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"b160422f8103574425e2834130e169d84c94fa1d","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"d36e75f5669140b66515ad3a176ca6337bd80a5e","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"84783961cb8bdb36b4f41a02ce43aafc6d52b176","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"bc4e05ae66c9797a0972ac44326e69c5305e0020","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"af0ee8f04bea22cdb331fa3509e17f81b48938ad","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"9144f2c53a04465a6878172b523f640313c5559e","versionType":"git"},{"version":"1a37e412a0225fcba5587f24c0dfc7636efc8b69","status":"affected","lessThan":"6b222adeb9340306e2ff97127c76117abb9b3df8","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/ip_tunnels.h","net/ipv4/ip_tunnel.c","net/ipv6/ip6_gre.c","net/ipv6/ip6_tunnel.c","net/ipv6/sit.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.11","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","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":["include/net/ip_tunnels.h","net/ipv4/ip_tunnel.c","net/ipv6/ip6_gre.c","net/ipv6/ip6_tunnel.c","net/ipv6/sit.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/fb889a619723032140f5d983a3a34d25a5a2bed4"},{"url":"https://git.kernel.org/stable/c/b160422f8103574425e2834130e169d84c94fa1d"},{"url":"https://git.kernel.org/stable/c/d36e75f5669140b66515ad3a176ca6337bd80a5e"},{"url":"https://git.kernel.org/stable/c/84783961cb8bdb36b4f41a02ce43aafc6d52b176"},{"url":"https://git.kernel.org/stable/c/bc4e05ae66c9797a0972ac44326e69c5305e0020"},{"url":"https://git.kernel.org/stable/c/af0ee8f04bea22cdb331fa3509e17f81b48938ad"},{"url":"https://git.kernel.org/stable/c/9144f2c53a04465a6878172b523f640313c5559e"},{"url":"https://git.kernel.org/stable/c/6b222adeb9340306e2ff97127c76117abb9b3df8"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - Triggering the wrap requires locally creating a namespace stack of IP tunnel devices (ipip/gre/sit/ip6tnl via rtnetlink or SIOCADDTUNNEL) so bind/link-config can copy an uncapped needed_headroom, then sending packets through that stack. A remote peer cannot build that topology, so the attacker-controlled path is local.\nAC:L - The attacker fully controls tunnel creation, IFLA_IPTUN_LINK/parms.link stacking (or a netkit lower device with a large IFLA_NETKIT_HEADROOM), and the subsequent transmit. Each bind copies lower needed_headroom plus t_hlen until LL_RESERVED_SPACE exceeds 16-bit skb offsets; no race or uninfluenced victim state is required.\nPR:L - Creating and binding these tunnels needs CAP_NET_ADMIN, but rtnetlink uses netlink_ns_capable()/sk_ns_capable() against net->user_ns and ip_tunnel_ctl uses ns_capable(net->user_ns, CAP_NET_ADMIN), so an unprivileged user obtains it with unshare -Urn. Fallback tunl0/ip6tnl0 devices are created in every netns by default.\nUI:N - The attacker creates the stacked tunnels and generates the traffic that drives IP output/skb_cow_head; no other user or administrator action is required.\nS:U - The resulting skb header-offset wrap corrupts kernel heap in the same OS security authority. This is standard in-kernel privilege escalation, not a VM, IOMMU, or hypervisor boundary crossing.\nC:H - After pskb_expand_head adds a >64K nhead, u16 network_header wraps so skb->data points outside skb->head. Neighbour/flow-dissect paths then __skb_pull/read with a negative offset, producing the same unbounded KASAN use-after-free/OOB read as CVE-2024-26804/CVE-2025-40173.\nI:H - Post-wrap, skb_push/dev_hard_header and iptunnel_xmit/ip6_tnl_xmit write outer IP/GRE headers at the corrupted skb->data, giving an out-of-bounds write into unrelated kernel heap that can be used for control-flow hijacking.\nA:H - The wrapped offsets and subsequent out-of-bounds accesses reliably oops/panic (KASAN, skb_under_panic, or unmapped dereference), matching the confirmed crash impact of the earlier unbounded tunnel-headroom bugs."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:46:02.787Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"5.10.270"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"5.15.221"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"6.1.188"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"6.12.109"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.11","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-80978","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:21:45.426777Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:37.217Z"}}]}}}