CVE-2026-63983: net/sched: fix packet loop on netem when duplicate is on

criticalCVSS 9.8CVE-2026-63983

CSIRTS triage

vendor: Linux product: NetemOther

What: The vulnerability causes a packet loop when duplicate packets are present in netem.
Who is affected: Deployments using the netem feature in the Linux kernel.
Urgency: Remediation is critical due to the high CVSS score of 9.8, indicating severe potential impact.
Action: Update to the patched version of the kernel that resolves CVE-2026-63983.

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: critical — CVSS 9.8
Published: 2026-07-14
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-63983

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-2026-639830.17% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 6% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-63983	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

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

highUSN-8618-1: Linux kernel vulnerabilitiesubuntu
highUSN-8603-1: Linux kernel (Azure) vulnerabilitiesubuntu
highUSN-8593-1: Linux kernel vulnerabilitiesubuntu
unknownCVE-2026-63983: In the Linux kernel, the following vulnerability has been resolved: net/sched: fix packet loop…nvd

Recent advisories for net/sched

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-2026-64530: In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: Handle…nvd · 2026-07-26
unknownCVE-2026-64207: In the Linux kernel, the following vulnerability has been resolved: net/sched: dualpi2: fix GS…nvd · 2026-07-20
unknownCVE-2026-64012: In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_sfb: Replac…nvd · 2026-07-19
unknownCVE-2026-63983: In the Linux kernel, the following vulnerability has been resolved: net/sched: fix packet loop…nvd · 2026-07-19
unknownCVE-2026-63982: In the Linux kernel, the following vulnerability has been resolved: net/sched: Fix ethx:ingres…nvd · 2026-07-19
unknownCVE-2026-63981: In the Linux kernel, the following vulnerability has been resolved: net/sched: act_mirred: Fix…nvd · 2026-07-19