CVE-2026-63921 (GCVE-0-2026-63921)
Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-10-19 20:17
VLAI
EPSS
VEX
Title
ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().
Summary
In the Linux kernel, the following vulnerability has been resolved:
ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().
After patch 1/2 in this series, vti6_update() unlinks and relinks
the tunnel through t->net. vti6_siocdevprivate() still uses
dev_net(dev) for the collision lookup. For a tunnel moved through
IFLA_NET_NS_FD, dev_net(dev) is the new netns, not t->net.
SIOCCHGTUNNEL on a migrated tunnel then runs:
net = dev_net(dev) /* migrated netns */
t = vti6_locate(net, &p1, false) /* misses target in t->net */
...
t = netdev_priv(dev)
vti6_update(t, &p1, false) /* mutates t->net's hash */
A caller in the migrated netns picks params that match a tunnel
in the creation netns. The lookup in dev_net(dev) finds nothing.
vti6_update() prepends the migrated tunnel at the head of the
creation netns hash bucket for those params. Later lookups in
the creation netns resolve to the migrated device. xfrm receive
delivers the matched packets through a device the caller controls.
Reachable from an unprivileged user namespace (unshare --user
--map-root-user --net). Cross tenant scope on container hosts.
Switch the SIOCCHGTUNNEL path on a non fallback device to use
t->net for the lookup. The lookup now matches the netns
vti6_update() operates on.
Also add ns_capable(self->net->user_ns, CAP_NET_ADMIN) before
the lookup. The check at the top of the case is against
dev_net(dev)->user_ns, which after migration is the attacker's
netns. A caller there can pick params absent from self->net,
the lookup returns NULL, t becomes self, and vti6_update()
inserts the device into the creation netns hash. The new check
requires CAP_NET_ADMIN in the creation netns user_ns too.
SIOCADDTUNNEL and SIOCCHGTUNNEL on the fallback device keep
dev_net(dev), which equals init_net there.
Severity
8.8 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-16 15:33 UTC
CWE
- CWE-862 - Missing Authorization
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
61220ab349485d911083d0b7990ccd3db6c63297 , < 94ff740a7f9ef5c010784a325dca00cbf228f941
(git)
Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < df42ac708acc3399bbb6dc5ca16e0540adda7bbf (git) Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < 44d2ff7d2178503b93151140a45dfa2ad49c9906 (git) Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < 1acfb7d9c6fc7e209ed7789392697e97e03edd33 (git) Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < d2236348414bdd6558385f35aa7fdc9bf5634011 (git) Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < 853f6ea482dfcd3404bbef458ab4d68364eed838 (git) Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < 596f6354c96a891e58c04a09cbfb7b0d1ec00dab (git) Affected: 61220ab349485d911083d0b7990ccd3db6c63297 , < 8b484efd5cb4eeef9021a661e198edc5349dacf6 (git) |
guessed | |
| Linux | Linux |
Affected:
3.15
Unaffected: 0 , < 3.15 (semver) Unaffected: 5.10.259 , ≤ 5.10.* (semver) Unaffected: 5.15.210 , ≤ 5.15.* (semver) Unaffected: 6.1.176 , ≤ 6.1.* (semver) Unaffected: 6.6.143 , ≤ 6.6.* (semver) Unaffected: 6.12.93 , ≤ 6.12.* (semver) Unaffected: 6.18.35 , ≤ 6.18.* (semver) Unaffected: 7.0.12 , ≤ 7.0.* (semver) Unaffected: 7.1 , ≤ * (original_commit_for_fix) |
guessed |
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().\n\nAfter patch 1/2 in this series, vti6_update() unlinks and relinks\nthe tunnel through t-\u003enet. vti6_siocdevprivate() still uses\ndev_net(dev) for the collision lookup. For a tunnel moved through\nIFLA_NET_NS_FD, dev_net(dev) is the new netns, not t-\u003enet.\n\nSIOCCHGTUNNEL on a migrated tunnel then runs:\n\n net = dev_net(dev) /* migrated netns */\n t = vti6_locate(net, \u0026p1, false) /* misses target in t-\u003enet */\n ...\n t = netdev_priv(dev)\n vti6_update(t, \u0026p1, false) /* mutates t-\u003enet\u0027s hash */\n\nA caller in the migrated netns picks params that match a tunnel\nin the creation netns. The lookup in dev_net(dev) finds nothing.\nvti6_update() prepends the migrated tunnel at the head of the\ncreation netns hash bucket for those params. Later lookups in\nthe creation netns resolve to the migrated device. xfrm receive\ndelivers the matched packets through a device the caller controls.\n\nReachable from an unprivileged user namespace (unshare --user\n--map-root-user --net). Cross tenant scope on container hosts.\n\nSwitch the SIOCCHGTUNNEL path on a non fallback device to use\nt-\u003enet for the lookup. The lookup now matches the netns\nvti6_update() operates on.\n\nAlso add ns_capable(self-\u003enet-\u003euser_ns, CAP_NET_ADMIN) before\nthe lookup. The check at the top of the case is against\ndev_net(dev)-\u003euser_ns, which after migration is the attacker\u0027s\nnetns. A caller there can pick params absent from self-\u003enet,\nthe lookup returns NULL, t becomes self, and vti6_update()\ninserts the device into the creation netns hash. The new check\nrequires CAP_NET_ADMIN in the creation netns user_ns too.\n\nSIOCADDTUNNEL and SIOCCHGTUNNEL on the fallback device keep\ndev_net(dev), which equals init_net there."
}
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().\n\nAfter patch 1/2 in this series, vti6_update() unlinks and relinks\nthe tunnel through t-\u003enet. vti6_siocdevprivate() still uses\ndev_net(dev) for the collision lookup. For a tunnel moved through\nIFLA_NET_NS_FD, dev_net(dev) is the new netns, not t-\u003enet.\n\nSIOCCHGTUNNEL on a migrated tunnel then runs:\n\n net = dev_net(dev) /* migrated netns */\n t = vti6_locate(net, \u0026p1, false) /* misses target in t-\u003enet */\n ...\n t = netdev_priv(dev)\n vti6_update(t, \u0026p1, false) /* mutates t-\u003enet\u0027s hash */\n\nA caller in the migrated netns picks params that match a tunnel\nin the creation netns. The lookup in dev_net(dev) finds nothing.\nvti6_update() prepends the migrated tunnel at the head of the\ncreation netns hash bucket for those params. Later lookups in\nthe creation netns resolve to the migrated device. xfrm receive\ndelivers the matched packets through a device the caller controls.\n\nReachable from an unprivileged user namespace (unshare --user\n--map-root-user --net). Cross tenant scope on container hosts.\n\nSwitch the SIOCCHGTUNNEL path on a non fallback device to use\nt-\u003enet for the lookup. The lookup now matches the netns\nvti6_update() operates on.\n\nAlso add ns_capable(self-\u003enet-\u003euser_ns, CAP_NET_ADMIN) before\nthe lookup. The check at the top of the case is against\ndev_net(dev)-\u003euser_ns, which after migration is the attacker\u0027s\nnetns. A caller there can pick params absent from self-\u003enet,\nthe lookup returns NULL, t becomes self, and vti6_update()\ninserts the device into the creation netns hash. The new check\nrequires CAP_NET_ADMIN in the creation netns user_ns too.\n\nSIOCADDTUNNEL and SIOCCHGTUNNEL on the fallback device keep\ndev_net(dev), which equals init_net there."
}
],
"id": "CVE-2026-63921",
"lastModified": "2026-10-19T21:17:11.433",
"metrics": {
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"scope": "CHANGED",
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"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-63921",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-10-16T15:33:25.874966Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-07-19T16:17:10.300",
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},
{
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},
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},
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"url": "https://git.kernel.org/stable/c/94ff740a7f9ef5c010784a325dca00cbf228f941"
},
{
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"url": "https://git.kernel.org/stable/c/d2236348414bdd6558385f35aa7fdc9bf5634011"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/df42ac708acc3399bbb6dc5ca16e0540adda7bbf"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Awaiting Analysis",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-862"
}
],
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"type": "Secondary"
}
]
}
},
"redhat_vex": {
"aggregate_severity": "Important",
"current_release_date": "2026-10-14T12:34:36+00:00",
"cve": "CVE-2026-63921",
"id": "CVE-2026-63921",
"initial_release_date": "2026-07-19T00:00:00+00:00",
"product_status:fixed": "2122",
"product_status:known_affected": "50",
"product_status:known_not_affected": "14",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate()",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63921.json",
"version": "3"
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-63921",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-10-16T15:33:25.874966Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-862",
"description": "CWE-862 Missing Authorization",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-16T15:33:26.437Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"net/ipv6/ip6_vti.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
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"status": "affected",
"version": "61220ab349485d911083d0b7990ccd3db6c63297",
"versionType": "git"
},
{
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"status": "affected",
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"versionType": "git"
},
{
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"status": "affected",
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{
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],
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"vendor": "Linux",
"versions": [
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"version": "3.15"
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{
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"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "5.10.259",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "5.15.210",
"versionType": "semver"
},
{
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"status": "unaffected",
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"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
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{
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{
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"status": "unaffected",
"version": "7.0.12",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "7.1",
"versionType": "original_commit_for_fix"
}
]
}
],
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"vulnerable": true
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"descriptions": [
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().\n\nAfter patch 1/2 in this series, vti6_update() unlinks and relinks\nthe tunnel through t-\u003enet. vti6_siocdevprivate() still uses\ndev_net(dev) for the collision lookup. For a tunnel moved through\nIFLA_NET_NS_FD, dev_net(dev) is the new netns, not t-\u003enet.\n\nSIOCCHGTUNNEL on a migrated tunnel then runs:\n\n net = dev_net(dev) /* migrated netns */\n t = vti6_locate(net, \u0026p1, false) /* misses target in t-\u003enet */\n ...\n t = netdev_priv(dev)\n vti6_update(t, \u0026p1, false) /* mutates t-\u003enet\u0027s hash */\n\nA caller in the migrated netns picks params that match a tunnel\nin the creation netns. The lookup in dev_net(dev) finds nothing.\nvti6_update() prepends the migrated tunnel at the head of the\ncreation netns hash bucket for those params. Later lookups in\nthe creation netns resolve to the migrated device. xfrm receive\ndelivers the matched packets through a device the caller controls.\n\nReachable from an unprivileged user namespace (unshare --user\n--map-root-user --net). Cross tenant scope on container hosts.\n\nSwitch the SIOCCHGTUNNEL path on a non fallback device to use\nt-\u003enet for the lookup. The lookup now matches the netns\nvti6_update() operates on.\n\nAlso add ns_capable(self-\u003enet-\u003euser_ns, CAP_NET_ADMIN) before\nthe lookup. The check at the top of the case is against\ndev_net(dev)-\u003euser_ns, which after migration is the attacker\u0027s\nnetns. A caller there can pick params absent from self-\u003enet,\nthe lookup returns NULL, t becomes self, and vti6_update()\ninserts the device into the creation netns hash. The new check\nrequires CAP_NET_ADMIN in the creation netns user_ns too.\n\nSIOCADDTUNNEL and SIOCCHGTUNNEL on the fallback device keep\ndev_net(dev), which equals init_net there."
}
],
"metrics": [
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"baseScore": 8.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
"version": "3.1"
},
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"value": "AV:L - Exploitation requires a local ioctl(SIOCCHGTUNNEL) on a migrated vti6 netdev via socket/dev_ioctl; the bug is in vti6_siocdevprivate(), not in remote packet reception.\nAC:L - The attacker fully controls namespace creation, tunnel migration (IFLA_NET_NS_FD), and ioctl parameters to collide with a victim tunnel; the commit documents a deterministic, reproducible sequence with no uncontrollable race.\nPR:L - Only CAP_NET_ADMIN in the migrated (attacker) network namespace is required, obtainable via unprivileged user namespaces (unshare --user --map-root-user --net); the missing check against the creation namespace\u0027s user_ns is the core flaw.\nUI:N - No victim interaction is needed; the attacker performs all setup steps (create/migrate tunnel, issue SIOCCHGTUNNEL) autonomously.\nS:C - The attack hijacks IPsec/XFRM traffic destined for tunnels in a different tenant\u0027s network namespace on container hosts, crossing container/tenant security boundaries rather than staying within the attacker\u0027s own scope.\nC:H - After hash poisoning, xfrm receive delivers matched/decapsulated packets to the attacker-controlled netdev, enabling interception of victim VPN/IPsec traffic including potentially sensitive plaintext after decryption.\nI:H - The attacker gains control over which netdev receives victim tunnel traffic and can read, drop, or forward/modify decapsulated packets, constituting unauthorized manipulation of another tenant\u0027s network data path.\nA:H - Hijacking the creation-namespace hash bucket causes the legitimate victim tunnel to stop receiving matched traffic, producing denial of service to the victim\u0027s IPsec connectivity."
}
]
}
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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{
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},
{
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},
{
"url": "https://git.kernel.org/stable/c/8b484efd5cb4eeef9021a661e198edc5349dacf6"
}
],
"title": "ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().",
"x_generator": {
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"cveMetadata": {
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"cveId": "CVE-2026-63921",
"datePublished": "2026-07-19T14:55:23.539Z",
"dateReserved": "2026-07-19T07:54:57.020Z",
"dateUpdated": "2026-10-19T20:17:56.432Z",
"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
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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.