{"id":"CVE-2024-26804","state":"PUBLISHED","title":"net: ip_tunnel: prevent perpetual headroom growth","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ip_tunnel: prevent perpetual headroom growth\n\nsyzkaller triggered following kasan splat:\nBUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170\nRead of size 1 at addr ffff88812fb4000e by task syz-executor183/5191\n[..]\n kasan_report+0xda/0x110 mm/kasan/report.c:588\n __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170\n skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline]\n ___skb_get_hash net/core/flow_dissector.c:1791 [inline]\n __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856\n skb_get_hash include/linux/skbuff.h:1556 [inline]\n ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748\n ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308\n __netdev_start_xmit include/linux/netdevice.h:4940 [inline]\n netdev_start_xmit include/linux/netdevice.h:4954 [inline]\n xmit_one net/core/dev.c:3548 [inline]\n dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564\n __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349\n dev_queue_xmit include/linux/netdevice.h:3134 [inline]\n neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592\n ...\n ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235\n ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323\n ..\n iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82\n ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831\n ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665\n __netdev_start_xmit include/linux/netdevice.h:4940 [inline]\n netdev_start_xmit include/linux/netdevice.h:4954 [inline]\n xmit_one net/core/dev.c:3548 [inline]\n dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564\n ...\n\nThe splat occurs because skb->data points past skb->head allocated area.\nThis is because neigh layer does:\n  __skb_pull(skb, skb_network_offset(skb));\n\n... but skb_network_offset() returns a negative offset and __skb_pull()\narg is unsigned.  IOW, we skb->data gets \"adjusted\" by a huge value.\n\nThe negative value is returned because skb->head and skb->data distance is\nmore than 64k and skb->network_header (u16) has wrapped around.\n\nThe bug is in the ip_tunnel infrastructure, which can cause\ndev->needed_headroom to increment ad infinitum.\n\nThe syzkaller reproducer consists of packets getting routed via a gre\ntunnel, and route of gre encapsulated packets pointing at another (ipip)\ntunnel.  The ipip encapsulation finds gre0 as next output device.\n\nThis results in the following pattern:\n\n1). First packet is to be sent out via gre0.\nRoute lookup found an output device, ipip0.\n\n2).\nip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future\noutput device, rt.dev->needed_headroom (ipip0).\n\n3).\nip output / start_xmit moves skb on to ipip0. which runs the same\ncode path again (xmit recursion).\n\n4).\nRouting step for the post-gre0-encap packet finds gre0 as output device\nto use for ipip0 encapsulated packet.\n\ntunl0->needed_headroom is then incremented based on the (already bumped)\ngre0 device headroom.\n\nThis repeats for every future packet:\n\ngre0->needed_headroom gets inflated because previous packets' ipip0 step\nincremented rt->dev (gre0) headroom, and ipip0 incremented because gre0\nneeded_headroom was increased.\n\nFor each subsequent packet, gre/ipip0->needed_headroom grows until\npost-expand-head reallocations result in a skb->head/data distance of\nmore than 64k.\n\nOnce that happens, skb->network_header (u16) wraps around when\npskb_expand_head tries to make sure that skb_network_offset() is unchanged\nafter the headroom expansion/reallocation.\n\nAfter this skb_network_offset(skb) returns a different (and negative)\nresult post headroom expansion.\n\nThe next trip to neigh layer (or anything else that would __skb_pull the\nnetwork header) makes skb->data point to a memory location outside\nskb->head area.\n\nv2: Cap the needed_headroom update to an arbitarily chosen upperlimit to\nprevent perpetual increase instead of dropping the headroom increment\ncompletely.","publishedAt":"2024-04-04T08:20:31.305Z","updatedAt":"2026-08-12T17:39:59.942Z","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":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"f81e94d2dcd2397137edcb8b85f4c5bed5d22383","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"2e95350fe9db9d53c701075060ac8ac883b68aee","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"afec0c5cd2ed71ca95a8b36a5e6d03333bf34282","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"ab63de24ebea36fe73ac7121738595d704b66d96","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"049d7989c67e8dd50f07a2096dbafdb41331fb9b","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f","versionType":"git"},{"version":"03017375b0122453e6dda833ff7bd4191915def5","status":"affected","versionType":"git"},{"version":"2.6.33.2","status":"affected","lessThan":"2.6.34","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.34","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.34","versionType":"semver"},{"version":"5.4.271","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.212","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.151","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.81","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.21","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.7.9","status":"unaffected","lessThanOrEqual":"6.7.*","versionType":"semver"},{"version":"6.8","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel.c"]}],"references":["https://git.kernel.org/stable/c/f81e94d2dcd2397137edcb8b85f4c5bed5d22383","https://git.kernel.org/stable/c/2e95350fe9db9d53c701075060ac8ac883b68aee","https://git.kernel.org/stable/c/afec0c5cd2ed71ca95a8b36a5e6d03333bf34282","https://git.kernel.org/stable/c/ab63de24ebea36fe73ac7121738595d704b66d96","https://git.kernel.org/stable/c/a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9","https://git.kernel.org/stable/c/049d7989c67e8dd50f07a2096dbafdb41331fb9b","https://git.kernel.org/stable/c/5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f","https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:07:10.607Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2024/26xxx/CVE-2024-26804.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2024-26804","state":"PUBLISHED","datePublished":"2024-04-04T08:20:31.305Z","dateUpdated":"2026-08-12T17:39:59.942Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-02-19T14:20:24.179Z"},"containers":{"cna":{"title":"net: ip_tunnel: prevent perpetual headroom growth","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ip_tunnel: prevent perpetual headroom growth\n\nsyzkaller triggered following kasan splat:\nBUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170\nRead of size 1 at addr ffff88812fb4000e by task syz-executor183/5191\n[..]\n kasan_report+0xda/0x110 mm/kasan/report.c:588\n __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170\n skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline]\n ___skb_get_hash net/core/flow_dissector.c:1791 [inline]\n __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856\n skb_get_hash include/linux/skbuff.h:1556 [inline]\n ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748\n ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308\n __netdev_start_xmit include/linux/netdevice.h:4940 [inline]\n netdev_start_xmit include/linux/netdevice.h:4954 [inline]\n xmit_one net/core/dev.c:3548 [inline]\n dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564\n __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349\n dev_queue_xmit include/linux/netdevice.h:3134 [inline]\n neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592\n ...\n ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235\n ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323\n ..\n iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82\n ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831\n ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665\n __netdev_start_xmit include/linux/netdevice.h:4940 [inline]\n netdev_start_xmit include/linux/netdevice.h:4954 [inline]\n xmit_one net/core/dev.c:3548 [inline]\n dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564\n ...\n\nThe splat occurs because skb->data points past skb->head allocated area.\nThis is because neigh layer does:\n  __skb_pull(skb, skb_network_offset(skb));\n\n... but skb_network_offset() returns a negative offset and __skb_pull()\narg is unsigned.  IOW, we skb->data gets \"adjusted\" by a huge value.\n\nThe negative value is returned because skb->head and skb->data distance is\nmore than 64k and skb->network_header (u16) has wrapped around.\n\nThe bug is in the ip_tunnel infrastructure, which can cause\ndev->needed_headroom to increment ad infinitum.\n\nThe syzkaller reproducer consists of packets getting routed via a gre\ntunnel, and route of gre encapsulated packets pointing at another (ipip)\ntunnel.  The ipip encapsulation finds gre0 as next output device.\n\nThis results in the following pattern:\n\n1). First packet is to be sent out via gre0.\nRoute lookup found an output device, ipip0.\n\n2).\nip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future\noutput device, rt.dev->needed_headroom (ipip0).\n\n3).\nip output / start_xmit moves skb on to ipip0. which runs the same\ncode path again (xmit recursion).\n\n4).\nRouting step for the post-gre0-encap packet finds gre0 as output device\nto use for ipip0 encapsulated packet.\n\ntunl0->needed_headroom is then incremented based on the (already bumped)\ngre0 device headroom.\n\nThis repeats for every future packet:\n\ngre0->needed_headroom gets inflated because previous packets' ipip0 step\nincremented rt->dev (gre0) headroom, and ipip0 incremented because gre0\nneeded_headroom was increased.\n\nFor each subsequent packet, gre/ipip0->needed_headroom grows until\npost-expand-head reallocations result in a skb->head/data distance of\nmore than 64k.\n\nOnce that happens, skb->network_header (u16) wraps around when\npskb_expand_head tries to make sure that skb_network_offset() is unchanged\nafter the headroom expansion/reallocation.\n\nAfter this skb_network_offset(skb) returns a different (and negative)\nresult post headroom expansion.\n\nThe next trip to neigh layer (or anything else that would __skb_pull the\nnetwork header) makes skb->data point to a memory location outside\nskb->head area.\n\nv2: Cap the needed_headroom update to an arbitarily chosen upperlimit to\nprevent perpetual increase instead of dropping the headroom increment\ncompletely."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"f81e94d2dcd2397137edcb8b85f4c5bed5d22383","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"2e95350fe9db9d53c701075060ac8ac883b68aee","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"afec0c5cd2ed71ca95a8b36a5e6d03333bf34282","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"ab63de24ebea36fe73ac7121738595d704b66d96","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"049d7989c67e8dd50f07a2096dbafdb41331fb9b","versionType":"git"},{"version":"243aad830e8a4cdda261626fbaeddde16b08d04a","status":"affected","lessThan":"5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f","versionType":"git"},{"version":"03017375b0122453e6dda833ff7bd4191915def5","status":"affected","versionType":"git"},{"version":"2.6.33.2","status":"affected","lessThan":"2.6.34","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.34","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.34","versionType":"semver"},{"version":"5.4.271","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.212","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.151","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.81","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.21","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.7.9","status":"unaffected","lessThanOrEqual":"6.7.*","versionType":"semver"},{"version":"6.8","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/f81e94d2dcd2397137edcb8b85f4c5bed5d22383"},{"url":"https://git.kernel.org/stable/c/2e95350fe9db9d53c701075060ac8ac883b68aee"},{"url":"https://git.kernel.org/stable/c/afec0c5cd2ed71ca95a8b36a5e6d03333bf34282"},{"url":"https://git.kernel.org/stable/c/ab63de24ebea36fe73ac7121738595d704b66d96"},{"url":"https://git.kernel.org/stable/c/a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9"},{"url":"https://git.kernel.org/stable/c/049d7989c67e8dd50f07a2096dbafdb41331fb9b"},{"url":"https://git.kernel.org/stable/c/5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f"}],"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 - The attacker must locally configure a two-device ip_tunnel routing cycle (gre0 ↔ tunl0) via rtnetlink/ioctl and then transmit packets through a local socket; a remote peer cannot create the tunnel topology that drives the headroom growth.\nAC:L - The headroom inflation is fully deterministic — each transmitted packet monotonically increases dev->needed_headroom until the u16 network_header wraps, with no race and no dependence on memory layout the attacker cannot influence. The required ipip/gre modules are standard on virtually all distributions.\nPR:L - An unprivileged user gains CAP_NET_ADMIN over a private netns via unshare -Urn, since rtnetlink checks netlink_net_capable() against the netns owning user_ns, and tunl0/gre0 fallback devices are auto-created in every netns because sysctl_fb_tunnels_only_for_init_net defaults to 0.\nUI:N - The attacker performs the entire setup and packet transmission alone; no victim action or interaction is required.\nS:U - The corruption occurs in kernel memory within the same security authority; no VM, IOMMU, or hypervisor boundary is crossed.\nC:H - After the offset overflow skb->data points ~4GB away in the kernel direct map, producing the syzbot-confirmed KASAN out-of-bounds/use-after-free read in __skb_flow_dissect, and the resulting packet's payload is read from that arbitrary kernel memory and transmitted to the attacker-chosen tunnel destination — up to ~64KB of kernel memory disclosure.\nI:H - skb_push() only validates data < head, so iptunnel_xmit() writes a 20-byte IP header (with attacker-controlled saddr/daddr/tos/ttl) plus the GRE header and attacker-chosen GRE key into out-of-bounds kernel memory, giving a partially controlled write primitive suitable for corrupting adjacent kernel objects.\nA:H - The confirmed use-after-free/out-of-bounds access reliably causes a KASAN report, oops, or panic (unmapped-address dereference or skb_under_panic), and the unbounded needed_headroom growth also forces ever-larger skb reallocations."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T11:27:24.842Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"5.4.271"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"5.10.212"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"5.15.151"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"6.1.81"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"6.6.21"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"6.7.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.34","versionEndExcluding":"6.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.33.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-12T17:39:19.030766Z","id":"CVE-2024-26804","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-416","type":"CWE","lang":"en","description":"CWE-416 Use After Free"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-12T17:39:59.942Z"}},{"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/f81e94d2dcd2397137edcb8b85f4c5bed5d22383","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/2e95350fe9db9d53c701075060ac8ac883b68aee","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/afec0c5cd2ed71ca95a8b36a5e6d03333bf34282","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/ab63de24ebea36fe73ac7121738595d704b66d96","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/049d7989c67e8dd50f07a2096dbafdb41331fb9b","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f","tags":["x_transferred"]},{"url":"https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html","tags":["x_transferred"]}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2024-08-02T00:14:13.557Z"}}]}}}