CVE-2026-89563 (GCVE-0-2026-89563)
Vulnerability from cvelistv5 – Published: 2026-09-11 19:44 – Updated: 2026-10-19 08:48
VLAI
EPSS
VEX
Title
ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()
Summary
In the Linux kernel, the following vulnerability has been resolved:
ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()
ip6_tnl_xmit() may need to expand headroom before it can push the
outer IPv6 and optional encap headers. It currently does that with
skb_realloc_headroom(), copies skb->sk ownership, consumes the original
skb, and then continues processing with the replacement skb kept only in
its local variable.
That is safe only if the helper cannot fail afterwards. But this helper
still has post-reallocation error exits. collect_md tunnels reject
non-NONE encap after the replacement, and ip6_tnl_encap() can also fail
later. In those cases the helper returns an error to its callers while
the caller still only has the original skb pointer.
Both ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on
error, so they can end up freeing an skb that ip6_tnl_xmit() already
consumed.
Use skb_cow_head() instead. It provides the required headroom and
writability without privately replacing the caller-owned skb, so later
error returns cannot leave callers with a stale pointer.
The Ethernet users, ip6gretap and ip6erspan, clear IFF_TX_SKB_SHARING
and already call skb_cow_head() before entering ip6_tnl_xmit(). They do
not rely on the removed skb_shared() reallocation. This also makes the
IPv6 tunnel path consistent with ip_tunnel_xmit().
Severity
7.8 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-16 19:24 UTC
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
058214a4d1dfefed9f01a277fadd3590acb5f990 , < 6e8eff8ed13b14708bc39f170144eacde494aac6
(git)
Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < dc1a319a4815c074914e2812e0e9cd0164ca682b (git) Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < 629d5557e635cdbc109a14ed913ba5a540e3f79a (git) Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < defa0adeff132cc90ed66915b9a104d9393e1e54 (git) Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < 37df5bc6b5ccad88c2faa0f5466f150178882b74 (git) Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < b36dfd6e8cff00cea81c11cc0af88d1564763461 (git) Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < 8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52 (git) Affected: 058214a4d1dfefed9f01a277fadd3590acb5f990 , < 87f21b59ddc618eff9670c174842964ad65fdade (git) |
guessed | |
| Linux | Linux |
Affected:
4.7
Unaffected: 0 , < 4.7 (semver) Unaffected: 5.10.270 , ≤ 5.10.* (semver) Unaffected: 5.15.221 , ≤ 5.15.* (semver) Unaffected: 6.1.188 , ≤ 6.1.* (semver) Unaffected: 6.6.157 , ≤ 6.6.* (semver) Unaffected: 6.12.109 , ≤ 6.12.* (semver) Unaffected: 6.18.50 , ≤ 6.18.* (semver) Unaffected: 7.2.4 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix) |
guessed |
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"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."
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"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-\u003esk 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()."
}
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"id": "CVE-2026-89563",
"lastModified": "2026-10-19T09:17:52.040",
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"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"url": "https://git.kernel.org/stable/c/87f21b59ddc618eff9670c174842964ad65fdade"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/8fc56ca49fc0ee1725b55c67bb43ab0dd01f3f52"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/b36dfd6e8cff00cea81c11cc0af88d1564763461"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/dc1a319a4815c074914e2812e0e9cd0164ca682b"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/defa0adeff132cc90ed66915b9a104d9393e1e54"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Received"
}
},
"redhat_vex": {
"aggregate_severity": "Important",
"current_release_date": "2026-11-04T23:58:50+00:00",
"cve": "CVE-2026-89563",
"id": "CVE-2026-89563",
"initial_release_date": "2026-09-11T00:00:00+00:00",
"product_status:known_affected": "158",
"product_status:known_not_affected": "42",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89563.json",
"version": "3"
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-89563",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-10-16T19:24:12.096672Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-10-16T19:24:12.677Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"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": "6e8eff8ed13b14708bc39f170144eacde494aac6",
"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
"versionType": "git"
},
{
"lessThan": "dc1a319a4815c074914e2812e0e9cd0164ca682b",
"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
"versionType": "git"
},
{
"lessThan": "629d5557e635cdbc109a14ed913ba5a540e3f79a",
"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
"versionType": "git"
},
{
"lessThan": "defa0adeff132cc90ed66915b9a104d9393e1e54",
"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
"versionType": "git"
},
{
"lessThan": "37df5bc6b5ccad88c2faa0f5466f150178882b74",
"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
"versionType": "git"
},
{
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"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
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},
{
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"status": "affected",
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},
{
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"status": "affected",
"version": "058214a4d1dfefed9f01a277fadd3590acb5f990",
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}
]
},
{
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"product": "Linux",
"programFiles": [
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],
"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": "5.10.*",
"status": "unaffected",
"version": "5.10.270",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.221",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.188",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.157",
"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",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.10.270",
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"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.15.221",
"versionStartIncluding": "4.7",
"vulnerable": true
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{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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},
{
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"versionEndExcluding": "6.18.50",
"versionStartIncluding": "4.7",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.2.4",
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{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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}
],
"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-\u003esk 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."
}
]
}
],
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"dateUpdated": "2026-10-19T08:48:56.784Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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},
{
"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"
}
}
},
"cveMetadata": {
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"assignerShortName": "Linux",
"cveId": "CVE-2026-89563",
"datePublished": "2026-09-11T19:44:34.375Z",
"dateReserved": "2026-09-11T19:38:34.725Z",
"dateUpdated": "2026-10-19T08:48:56.784Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.