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Linux KernelOperating system · Linux

CVE-2026-53221

CRITICAL · 9.8 CVSS v3.1 Published 2026-06-25
Fix available
A fix is available. Upgrade to 5.10.259 / 5.15.210 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

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: fix incorrect tunnel matching in vti6_tnl_lookup() In vti6_tnl_lookup(), when an exact match for a tunnel fails, the code falls back to searching for wildcard tunnels: - Tunnels matching the packet's local address, with any remote address wildcard remote). - Tunnels matching the packet's remote address, with any local address (wildcard local). However, vti6 stores all these different types of tunnels in the same hash table (ip6n->tnls_r_l) prone to hash collisions. The bug is that the fallback search loops in vti6_tnl_lookup() were missing checks to ensure that the candidate tunnel actually has a wildcard address.

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

In vti6_tnl_lookup(), the fallback search for wildcard tunnels lacks validation to confirm candidate tunnels actually have wildcard addresses. Since all tunnel types (exact match, wildcard remote, wildcard local) are stored in the same hash table (ip6n->tnls_r_l), this can cause incorrect tunnel matching, potentially allowing traffic to be routed through unintended tunnels or bypassing tunnel security controls.

MitigationApply the kernel patch that adds proper wildcard address validation checks in the vti6_tnl_lookup() fallback loops to ensure only tunnels with matching wildcard configuration are returned.

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

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 3.19, < 5.10.259>= 5.11, < 5.15.210>= 5.16, < 6.1.176>= 6.2, < 6.6.143>= 6.7, < 6.12.94>= 6.13, < 6.18.36>= 6.19, < 7.0.13= 7.1

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 kernel version
    Run `uname -r` to obtain the running kernel version, then compare it against the affected ranges: >= 3.19, < 5.10.259; >= 5.11, < 5.15.210; >= 5.16, < 6.1.176; >= 6.2, < 6.6.143; >= 6.7, < 6.12.94; >= 6.13, < 6.18.36; >= 6.19, < 7.0.13; = 7.1
    Affected if The kernel version falls within any of the listed affected ranges
  2. Identify IPv6 VTI tunnel interfaces
    Run `ip -6 tunnel show` or examine `/proc/net/if_inet6` to list active IPv6 tunnel interfaces. VTI6 tunnels typically appear as 'vti6' type in the output
    Affected if Any vti6 tunnel interfaces are configured on the system
  3. Verify tunnel configuration has wildcard addresses
    For each vti6 tunnel identified, run `ip -6 tunnel show <tunnel-name>` to inspect the local and remote address configuration. Look for tunnels where local or remote addresses are set to :: (any) or missing, indicating wildcard configuration
    Affected if The vti6 tunnel uses wildcard addresses (:: or empty) for local or remote endpoints
  4. Check for multiple tunnel types in same hash table
    Examine the kernel's tunnel hash table by checking `/proc/net/ip6_vti` or using `ip -6 link show type vti6` to see all vti6 tunnels. The vulnerability exists because exact match, wildcard remote, and wildcard local tunnels coexist in `ip6n->tnls_r_l`
    Affected if Multiple vti6 tunnels exist with mixed exact and wildcard address configurations

The system is affected if it runs a kernel version in the affected ranges AND has vti6 tunnel interfaces configured with wildcard address settings.

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
Upgrade available Upgrade to 5.10.259 / 5.15.210 / 6.1.176 or later
Fixed in 5.10.2595.15.2106.1.176
Vendor patch git.kernel.org →
Interim mitigation

Apply the kernel patch that adds proper wildcard address validation checks in the vti6_tnl_lookup() fallback loops to ensure only tunnels with matching wildcard configuration are returned.

Recommended fix High confidence

Linux kernel 5.10.259, 5.15.210, 6.1.176, or 6.6.143 (depending on which major version branch you are on)

  1. Identify the currently running Linux kernel version using 'uname -r'
  2. Determine which version range your current kernel falls into from the affected ranges: >= 3.19 and < 5.10.259, >= 5.11 and < 5.15.210, >= 5.16 and < 6.1.176, or >= 6.2 and < 6.6.143
  3. Upgrade the Linux kernel to a version at or above the first fixed version in your range: 5.10.259, 5.15.210, 6.1.176, or 6.6.143 respectively
  4. Update bootloader configuration if necessary (e.g., update-grub for GRUB2)
  5. Reboot the system into the new kernel
  6. Verify the kernel version after reboot with 'uname -r' to confirm the fix is applied
Caveat Kernel upgrades may require rebuilding out-of-tree kernel modules; ensure driver compatibility before rebooting

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

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation2.0 h
  • Implementation6.0 h
  • Testing8.0 h
  • Review / QA3.0 h
19.0 hours of engineering $3,220
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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-2026-53221 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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