CVE-2026-80634: netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag

lowCVSS 2.5CVE-2026-80634

CSIRTS triage

vendor: Linux product: Linux kernel Denial of service

What: The netfilter flowtable processing causes an integer underflow in num_encaps counter during bridge VLAN untag operations.
Who is affected: Linux systems with netfilter flowtable and bridge VLAN configuration enabled.
Urgency: Low priority; integer underflow is a low-severity denial of service risk.
Action: Apply kernel security patch when available or review netfilter flowtable configuration.

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: low — CVSS 2.5
Published: 2026-08-11
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-80634

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-2026-806340.38% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 31% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-80634	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for netfilter

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.

criticalCVE-2026-80668: In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_ex…nvd · 2026-08-28
highCVE-2026-80664: In the Linux kernel, the following vulnerability has been resolved: netfilter: xt_nat: reject …nvd · 2026-08-28
highCVE-2026-80637: In the Linux kernel, the following vulnerability has been resolved: netfilter: synproxy: fix u…nvd · 2026-08-28
unknownCVE-2026-80636: In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: reve…nvd · 2026-08-28
criticalCVE-2026-80634: In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: avoi…nvd · 2026-08-28
criticalCVE-2026-80603: In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_ir…nvd · 2026-08-28