CVE-2026-63921High· 8.8▾ TwilightIn 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() …
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 48.4 · likelihood 0 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Oct 16.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
0.2%
Last analysed / modified upstream
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.
Linux >= 61220ab349485d911083d0b7990ccd3db6c63297 < 94ff740a7f9ef5c010784a325dca00cbf228f941Linux >= 61220ab349485d911083d0b7990ccd3db6c63297 < df42ac708acc3399bbb6dc5ca16e0540adda7bbfLinux >= 61220ab349485d911083d0b7990ccd3db6c63297 < 44d2ff7d2178503b93151140a45dfa2ad49c9906Linux >= 61220ab349485d911083d0b7990ccd3db6c63297 < 1acfb7d9c6fc7e209ed7789392697e97e03edd33Linux >= 61220ab349485d911083d0b7990ccd3db6c63297 < d2236348414bdd6558385f35aa7fdc9bf5634011Linux >= 61220ab349485d911083d0b7990ccd3db6c63297 < 853f6ea482dfcd3404bbef458ab4d68364eed838Linux >= 61220ab349485d911083d0b7990ccd3db6c63297 < 596f6354c96a891e58c04a09cbfb7b0d1ec00dabLinux >= 61220ab349485d911083d0b7990ccd3db6c63297 < 8b484efd5cb4eeef9021a661e198edc5349dacf6Linux 3.15Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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