CVE-2026-53221: ip6_vti: fix incorrect tunnel matching in vti6_tnl_lookup()

mediumCVSS 5.5CVE-2026-53221

CSIRTS triage

vendor: null product: nullOtheraffected: null

What: The vulnerability involves incorrect tunnel matching in the vti6_tnl_lookup function.
Who is affected: Deployments using the affected ip6_vti functionality.
Urgency: Remediation is medium due to the severity rating of 5.5.
Action: Apply the patch for CVE-2026-53221.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 5.5
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-53221

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-532210.56% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 43% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-53221	coverage & exploitation status	NVD · CVE.org

Recent advisories for ip6_vti

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-52909: ip6_vti: set netns_immutable on the fallback device.msrc · 2026-06-09