CVE-2026-63921

Estado: Pendiente de análisisAlta (8.8)—

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:

A caller in the migrated netns picks params that match a tunnel in the creation netns.

Leer descripción completaMostrar menos

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.

Detalles técnicos trazas, registros y código del informe original

  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 */

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Puntuación base: 8.8

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.18%
Percentil entre todas las CVEs puntuadas: 7
Fecha de la puntuación: 6/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1068 Exploitation for Privilege Escalationprivilege escalation85 %
Impacto principalT1574.008 Path Interception by Search Order Hijackingstealth · execution75 %
Impacto secundarioT1548.004 Elevated Execution with Promptprivilege escalation70 %

Escalada de privilegios local desde user namespace no privilegiado (unshare) mediante control de parámetros de túnel VTI6 para secuestrar dispositivo de red en netns privilegiado y redirigir tráfico xfrm.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Execution Prevention Threat Intelligence Program Restrict File and Directory Permissions Audit Application Isolation and Sandboxing Exploit Protection

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux Kernel^AI

Referencias

JSON original (NVD)

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  "id": "CVE-2026-63921",
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  "vulnStatus": "Awaiting Analysis",
  "descriptions": [
    {
      "lang": "en",
      "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->net. 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->net.\n\nSIOCCHGTUNNEL on a migrated tunnel then runs:\n\n  net = dev_net(dev)                    /* migrated netns */\n  t   = vti6_locate(net, &p1, false)    /* misses target in t->net */\n  ...\n  t   = netdev_priv(dev)\n  vti6_update(t, &p1, false)            /* mutates t->net's 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->net for the lookup. The lookup now matches the netns\nvti6_update() operates on.\n\nAlso add ns_capable(self->net->user_ns, CAP_NET_ADMIN) before\nthe lookup. The check at the top of the case is against\ndev_net(dev)->user_ns, which after migration is the attacker's\nnetns. A caller there can pick params absent from self->net,\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."
    }
  ],
  "lastModified": "2026-07-27T17:44:23.777",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}