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Advisory severityHigh7.0Red Hat Linux

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 10.0 Extended Update Support, Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support, Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-63921 Source published Source updated

VulniPulse record published Record updated

CVE-2026-63921
Affected products & platforms
Red Hat LinuxLinux Kernel
Open source advisory

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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 · high-confidence parse· fetched 7 days ago·verify at source

Fixed versions
  • kernel-0:6.12.0-211.55.1.el10_2
  • kernel-0:6.12.0-55.108.1.el10_0
  • kernel-rt-0:4.18.0-553.164.1.rt7.505.el8_10
  • kernel-0:4.18.0-553.164.1.el8_10
  • kernel-0:4.18.0-305.211.1.el8_4
  • kernel-0:4.18.0-372.220.1.el8_6
  • kernel-0:4.18.0-477.172.1.el8_8
  • kernel-0:5.14.0-687.49.1.el9_8
  • kernel-0:5.14.0-284.197.1.el9_2
  • kernel-rt-0:5.14.0-284.197.1.rt14.482.el9_2
  • kernel-0:5.14.0-427.154.1.el9_4
  • kernel-0:5.14.0-570.146.1.el9_6
  • RHSA-2026:67471
  • RHSA-2026:75560
  • RHSA-2026:68532
  • RHSA-2026:68531
  • RHSA-2026:77217
  • RHSA-2026:77216
  • RHSA-2026:77301
  • RHSA-2026:68570
  • RHSA-2026:80908
  • RHSA-2026:82860
  • RHSA-2026:77218
  • RHSA-2026:74174

Official advisory · high-confidence parse· fetched 7 days ago·verify at source

Mitigation

Upgrade to a fixed release: kernel-0:6.12.0-211.55.1.el10_2, kernel-0:6.12.0-55.108.1.el10_0, kernel-rt-0:4.18.0-553.164.1.rt7.505.el8_10, kernel-0:4.18.0-553.164.1.el8_10, kernel-0:4.18.0-305.211.1.el8_4, kernel-0:4.18.0-372.220.1.el8_6. That is the remediation for this advisory.

The vendor advisory may list interim mitigations or workarounds not captured here. Review it before change work.

Official advisory · high-confidence parse· fetched 7 days ago·verify at source

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