{"api_version":"1","generated_at":"2026-09-13T13:44:41+00:00","cve":"CVE-2026-89563","urls":{"html":"https://cve.report/CVE-2026-89563","api":"https://cve.report/api/cve/CVE-2026-89563.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-89563","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-89563"},"summary":{"title":"ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()\n\nip6_tnl_xmit() may need to expand headroom before it can push the\nouter IPv6 and optional encap headers. It currently does that with\nskb_realloc_headroom(), copies skb->sk ownership, consumes the original\nskb, and then continues processing with the replacement skb kept only in\nits local variable.\n\nThat is safe only if the helper cannot fail afterwards. But this helper\nstill has post-reallocation error exits. collect_md tunnels reject\nnon-NONE encap after the replacement, and ip6_tnl_encap() can also fail\nlater. In those cases the helper returns an error to its callers while\nthe caller still only has the original skb pointer.\n\nBoth ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on\nerror, so they can end up freeing an skb that ip6_tnl_xmit() already\nconsumed.\n\nUse skb_cow_head() instead. It provides the required headroom and\nwritability without privately replacing the caller-owned skb, so later\nerror returns cannot leave callers with a stale pointer.\n\nThe Ethernet users, ip6gretap and ip6erspan, clear IFF_TX_SKB_SHARING\nand already call skb_cow_head() before entering ip6_tnl_xmit(). They do\nnot rely on the removed skb_shared() reallocation. This also makes the\nIPv6 tunnel path consistent with ip_tunnel_xmit().","state":"PUBLISHED","assigner":"Linux","published_at":"2026-09-11 20:19:40","updated_at":"2026-09-13 07:17:22"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"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","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/37df5bc6b5ccad88c2faa0f5466f150178882b74","name":"https://git.kernel.org/stable/c/37df5bc6b5ccad88c2faa0f5466f150178882b74","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/87f21b59ddc618eff9670c174842964ad65fdade","name":"https://git.kernel.org/stable/c/87f21b59ddc618eff9670c174842964ad65fdade","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52","name":"https://git.kernel.org/stable/c/8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/b36dfd6e8cff00cea81c11cc0af88d1564763461","name":"https://git.kernel.org/stable/c/b36dfd6e8cff00cea81c11cc0af88d1564763461","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89563","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89563","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 058214a4d1dfefed9f01a277fadd3590acb5f990 37df5bc6b5ccad88c2faa0f5466f150178882b74 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 058214a4d1dfefed9f01a277fadd3590acb5f990 b36dfd6e8cff00cea81c11cc0af88d1564763461 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 058214a4d1dfefed9f01a277fadd3590acb5f990 8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 058214a4d1dfefed9f01a277fadd3590acb5f990 87f21b59ddc618eff9670c174842964ad65fdade git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4.7","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 4.7 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.109 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.50 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2.4 7.2.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.3-rc1 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"89563","cve":"CVE-2026-89563","epss":"0.001750000","percentile":"0.071990000","score_date":"2026-09-12","updated_at":"2026-09-13 00:08:17"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["net/ipv6/ip6_tunnel.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"37df5bc6b5ccad88c2faa0f5466f150178882b74","status":"affected","version":"058214a4d1dfefed9f01a277fadd3590acb5f990","versionType":"git"},{"lessThan":"b36dfd6e8cff00cea81c11cc0af88d1564763461","status":"affected","version":"058214a4d1dfefed9f01a277fadd3590acb5f990","versionType":"git"},{"lessThan":"8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52","status":"affected","version":"058214a4d1dfefed9f01a277fadd3590acb5f990","versionType":"git"},{"lessThan":"87f21b59ddc618eff9670c174842964ad65fdade","status":"affected","version":"058214a4d1dfefed9f01a277fadd3590acb5f990","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["net/ipv6/ip6_tunnel.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"4.7"},{"lessThan":"4.7","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.109","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.50","versionType":"semver"},{"lessThanOrEqual":"7.2.*","status":"unaffected","version":"7.2.4","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.3-rc1","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.109","versionStartIncluding":"4.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.50","versionStartIncluding":"4.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.4","versionStartIncluding":"4.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3-rc1","versionStartIncluding":"4.7","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()\n\nip6_tnl_xmit() may need to expand headroom before it can push the\nouter IPv6 and optional encap headers. It currently does that with\nskb_realloc_headroom(), copies skb->sk ownership, consumes the original\nskb, and then continues processing with the replacement skb kept only in\nits local variable.\n\nThat is safe only if the helper cannot fail afterwards. But this helper\nstill has post-reallocation error exits. collect_md tunnels reject\nnon-NONE encap after the replacement, and ip6_tnl_encap() can also fail\nlater. In those cases the helper returns an error to its callers while\nthe caller still only has the original skb pointer.\n\nBoth ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on\nerror, so they can end up freeing an skb that ip6_tnl_xmit() already\nconsumed.\n\nUse skb_cow_head() instead. It provides the required headroom and\nwritability without privately replacing the caller-owned skb, so later\nerror returns cannot leave callers with a stale pointer.\n\nThe Ethernet users, ip6gretap and ip6erspan, clear IFF_TX_SKB_SHARING\nand already call skb_cow_head() before entering ip6_tnl_xmit(). They do\nnot rely on the removed skb_shared() reallocation. This also makes the\nIPv6 tunnel path consistent with ip_tunnel_xmit()."}],"metrics":[{"cvssV3_1":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"scenarios":[{"lang":"en","value":"AV:L - The double-free is in ip6_tnl_xmit() on the ip6tnl/ip6gre transmit path. The reliable trigger is local: create a collect-metadata tunnel with FOU/GUE encap via rtnetlink, then push a packet through ip6_tnl_start_xmit() with tc tunnel_key+mirred. Ordinary remote packets on a working ip6tnl do not hit the post-realloc error path.\nAC:L - Once the collect-md device is created with non-NONE encap, any skb that needs headroom expansion takes skb_realloc_headroom(), consume_skb()s the original, then deterministically fails the collect_md/encap check so the caller kfree_skb()s the stale pointer. The published PoC reproduces this without a race or lucky layout.\nPR:L - Creating ip6tnl/ip6gre and tc filters needs CAP_NET_ADMIN, which an unprivileged user gets in their own user and network namespaces (unshare -Urn). The reporter confirmed this userns path; the resulting skb double-free is not confined to that namespace.\nUI:N - The attacker creates the tunnel, installs the tc redirect, and generates the packet themselves. No other user must mount a filesystem, open a file, or otherwise interact.\nS:U - The skb double-free corrupts kernel heap (skbuff_head_cache) on the same host. This is standard in-kernel memory corruption, not a VM escape, IOMMU/DMA bypass, or other cross-authority impact.\nC:H - consume_skb() frees the original skb and the caller later kfree_skb()s that stale pointer, a slab use-after-free/double-free. Reclaiming the skbuff_head_cache object yields an arbitrary kernel read primitive, so confidentiality impact is High.\nI:H - The same skb double-free/UAF is a heap primitive: the freed sk_buff can be sprayed and the second free or a later dereference used for an arbitrary write or control-flow hijack, so integrity impact is High.\nA:H - KASAN reports slab-use-after-free in ip6_tnl_start_xmit()/kfree_skb and the reproducer panics the kernel. Any skb double-free can oops or panic even if not fully exploited, so availability impact is High."}]}],"providerMetadata":{"dateUpdated":"2026-09-13T06:31:03.944Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/37df5bc6b5ccad88c2faa0f5466f150178882b74"},{"url":"https://git.kernel.org/stable/c/b36dfd6e8cff00cea81c11cc0af88d1564763461"},{"url":"https://git.kernel.org/stable/c/8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52"},{"url":"https://git.kernel.org/stable/c/87f21b59ddc618eff9670c174842964ad65fdade"}],"title":"ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-89563","datePublished":"2026-09-11T19:44:34.375Z","dateReserved":"2026-09-11T19:38:34.725Z","dateUpdated":"2026-09-13T06:31:03.944Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-11 20:19:40","lastModifiedDate":"2026-09-13 07:17:22","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"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","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"89563","Ordinal":"1","Title":"ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()","CVE":"CVE-2026-89563","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"89563","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()\n\nip6_tnl_xmit() may need to expand headroom before it can push the\nouter IPv6 and optional encap headers. It currently does that with\nskb_realloc_headroom(), copies skb->sk ownership, consumes the original\nskb, and then continues processing with the replacement skb kept only in\nits local variable.\n\nThat is safe only if the helper cannot fail afterwards. But this helper\nstill has post-reallocation error exits. collect_md tunnels reject\nnon-NONE encap after the replacement, and ip6_tnl_encap() can also fail\nlater. In those cases the helper returns an error to its callers while\nthe caller still only has the original skb pointer.\n\nBoth ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on\nerror, so they can end up freeing an skb that ip6_tnl_xmit() already\nconsumed.\n\nUse skb_cow_head() instead. It provides the required headroom and\nwritability without privately replacing the caller-owned skb, so later\nerror returns cannot leave callers with a stale pointer.\n\nThe Ethernet users, ip6gretap and ip6erspan, clear IFF_TX_SKB_SHARING\nand already call skb_cow_head() before entering ip6_tnl_xmit(). They do\nnot rely on the removed skb_shared() reallocation. This also makes the\nIPv6 tunnel path consistent with ip_tunnel_xmit().","Type":"Description","Title":"ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()"}]}}}