High [CVE-2026-63921] Use ip6_tnl.net in vti6_siocdevprivate
This high-severity Red Hat Linux advisory covers CVE-2026-63921 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8.
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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.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 6 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 6 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 6 days ago·verify at source
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