{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89563", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.725Z", "datePublished": "2026-09-11T19:44:34.375Z", "dateUpdated": "2026-10-19T08:48:56.784Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:48:56.784Z" }, "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": { "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 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." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ipv6/ip6_tunnel.c" ], "versions": [ { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "6e8eff8ed13b14708bc39f170144eacde494aac6", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "dc1a319a4815c074914e2812e0e9cd0164ca682b", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "629d5557e635cdbc109a14ed913ba5a540e3f79a", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "defa0adeff132cc90ed66915b9a104d9393e1e54", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "37df5bc6b5ccad88c2faa0f5466f150178882b74", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "b36dfd6e8cff00cea81c11cc0af88d1564763461", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52", "status": "affected", "versionType": "git" }, { "version": "058214a4d1dfefed9f01a277fadd3590acb5f990", "lessThan": "87f21b59ddc618eff9670c174842964ad65fdade", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ipv6/ip6_tunnel.c" ], "versions": [ { "version": "4.7", "status": "affected" }, { "version": "0", "lessThan": "4.7", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.270", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.221", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.188", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.157", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.109", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.50", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "5.10.270" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "5.15.221" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "6.1.188" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "6.6.157" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/6e8eff8ed13b14708bc39f170144eacde494aac6" }, { "url": "https://git.kernel.org/stable/c/dc1a319a4815c074914e2812e0e9cd0164ca682b" }, { "url": "https://git.kernel.org/stable/c/629d5557e635cdbc109a14ed913ba5a540e3f79a" }, { "url": "https://git.kernel.org/stable/c/defa0adeff132cc90ed66915b9a104d9393e1e54" }, { "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" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-89563", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "total" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:24:12.096672Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:44.202Z" } } ] } }