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VulnerabilityAwaiting classification

CVE-2026-63917

HIGH · 8.8 CVSS v3.1 Published 2026-07-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
Zero-click 5 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: ip6: vti: Use ip6_tnl.net in vti6_changelink(). ip netns add ns1 ip netns add ns2 ip -n ns1 link add vti6_test type vti6 remote ::1 local ::2 key 7 ip -n ns1 link set vti6_test netns ns2 ip -n ns2 link set vti6_test type vti6 remote ::3 local ::4 key 9 ip netns del ns2 ip netns del ns1 [ 132.495484] ------------[ cut here ]------------ [ 132.497609] kernel BUG at net/core/dev.c:12376! Commit 61220ab34948 ("vti6: Enable namespace changing") dropped NETIF_F_NETNS_LOCAL from vti6 devices. A vti6 tunnel can then move through IFLA_NET_NS_FD. After the move dev_net(dev) points at the new netns while t->net stays at the creation netns. vti6_changelink() and vti6_update() still use dev_net(dev) and dev_net(t->dev). They unlink from one per netns hash and relink into another. The creation netns is left with a stale entry. cleanup_net() of that netns later walks freed memory. Reachable from an unprivileged user namespace (unshare --user --map-root-user --net). Cross tenant scope on container hosts.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A use-after-free vulnerability in Linux kernel's IPv6 VTI (Virtual Tunnel Interface) where moving a vti6 interface between network namespaces leaves stale hash entries in the original namespace (dev_net(dev) points to new netns while t->net stays at creation netns). When vti6_changelink() or vti6_update() relinks the interface, the creation namespace is left with a stale entry that causes memory corruption during cleanup_net().

MitigationApply the kernel patch to use ip6_tnl.net (t->net) instead of dev_net(dev) in vti6_changelink() and vti6_update(). Until patched, restrict unprivileged user namespace creation on multi-tenant container hosts.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check if VTI6 tunnels exist
    Run 'ip -6 tunnel show' or 'ip link show type vti6' to list any configured VTI6 tunnels
    Affected if No VTI6 tunnels are configured, the system is not affected by this specific vulnerability path
  2. Check if VTI6 tunnels have been moved between network namespaces
    For each VTI6 tunnel, compare its creation namespace (where the tunnel was initially created) to its current device namespace using 'ip -6 tunnel show' and 'ip link show <device>'. Also check 'ip netns list' to identify multiple namespaces exist
    Affected if All VTI6 tunnels remain in their original creation namespace; the bug requires the tunnel to be moved to a different namespace than where it was created
  3. Check kernel version against the fix
    Run 'uname -r' to get the kernel version, then compare against the version that includes the fix for vti6_changelink() and vti6_update() using t->net instead of dev_net(dev)
    Affected if Kernel version is older than the version containing the CVE-2026-63917 fix; the vulnerability only exists in unpatched kernels
  4. Check if VTI6 kernel module is loaded
    Run 'lsmod | grep vti' or check /sys/module for vti6 or ip_vti modules
    Affected if VTI6 kernel support is not loaded or built into the kernel, the attack surface for this specific flaw does not exist

The system is affected only if: (1) a VTI6 tunnel was created in one network namespace and then moved to a different namespace, (2) the running kernel version predates the CVE-2026-63917 fix, and (3) VTI6 support is enabled in the kernel.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the kernel patch to use ip6_tnl.net (t->net) instead of dev_net(dev) in vti6_changelink() and vti6_update(). Until patched, restrict unprivileged user namespace creation on multi-tenant container hosts.

Recommended fix Moderate confidence

Upgrade to the kernel version containing the fix commit (the patch title indicates the fix: 'ip6: vti: Use ip6_tnl.net in vti6_changelink()')

  1. Identify the affected Linux kernel version running on the system
  2. Locate the source file containing vti6_changelink() and vti6_update() functions - typically net/ipv6/ip6_vti.c
  3. Apply the kernel patch that changes vti6_changelink() and vti6_update() to use the tunnel's stored network namespace (t->net or equivalent ip6_tnl.net) instead of dev_net(dev) for hash operations
  4. Recompile the kernel with the fix
  5. Reboot to the patched kernel
Caveat Kernel upgrade carries standard risks; ensure compatibility with existing system drivers and software before deploying

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-63917 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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