VulnerabilityPublished 19 Jul 2026Updated 15 Oct 2026

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

Affects Linux kernelSource GCVE Database

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Not known to be exploited.

Data as of 12 Nov 2026, 18:21 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 12 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

A fix has been implemented in the Linux kernel that uses the skb tc_depth field to safely prevent recursive packet duplication. Users should update their Linux kernel to the fixed version once available. No additional mitigation steps are indicated.

Description

A vulnerability in the Linux kernel's netem packet scheduler could cause a packet duplication loop when duplicate is enabled, potentially exhausting stack or memory resources. The issue arises because duplicated packets can be recursively duplicated again if multiple netem qdiscs are in the queueing tree. The flaw was due to improper handling of duplication state shared across concurrent enqueue paths. The fix involves marking packets with a depth counter to prevent repeated duplication safely.

Impact

This vulnerability can cause resource exhaustion (stack or memory) on affected Linux systems using netem with duplication enabled, potentially leading to denial of service conditions. There is no indication of code execution or privilege escalation. No known exploits in the wild have been reported.

Summary

CVE-2026-63983 addresses a packet loop vulnerability in the Linux kernel's netem scheduler when packet duplication is enabled. The vulnerability occurs because duplicated packets are re-enqueued at the root qdisc and can be duplicated again by another netem instance in the queueing tree, leading to recursive duplication until stack or memory exhaustion. The original guard used a per-qdisc state variable that was unsafe under concurrency. The fix replaces this with a packet-level depth counter (skb tc_depth) that increments on duplication and prevents further duplication if already set, ensuring safe operation regardless of queueing tree topology or concurrency.

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 12 Nov 2026, 18:21 UTC

Technical details

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