CVE-2026-63983
Received Received - Intake

Linux Kernel Netem Packet Loop Vulnerability

Publication date: 2026-07-19

Last updated on: 2026-07-19

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: fix packet loop on netem when duplicate is on When netem duplicates a packet it re-enqueues the copy at the root qdisc. If another netem sits in the tree the copy can be duplicated again, recursing until the stack or memory is exhausted. The original duplication guard temporarily zeroed q->duplicate around the re-enqueue, but that does not cover all cases because it is per-qdisc state shared across all concurrent enqueue paths and is not safe without additional locking. Use the skb tc_depth field introduced in an earlier patch: - increment it on the duplicate before re-enqueue - skip duplication for any skb whose tc_depth is already non-zero. This marks the packet itself rather than mutating qdisc state, therefore it is safe regardless of tree topology or concurrency.

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Meta Information

Published
2026-07-19
Last Modified
2026-07-19
Generated
2026-07-20
AI Q&A
2026-07-19
EPSS Evaluated
N/A
NVD
CVE-2026-63983
EUVD
EUVD-2026-45756

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
linux_kernel linux_kernel *
linux linux_kernel *

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a packet duplication issue in the netem network emulator. When a packet is duplicated, it can trigger recursive duplication if another netem instance exists in the network path, leading to a loop that exhausts system resources like memory or CPU.

Detection Guidance

This vulnerability involves a packet loop in the Linux kernel's netem qdisc when handling duplicate packets. Detection requires checking for excessive packet duplication or memory exhaustion in network traffic. Monitor system logs for kernel errors or crashes related to network processing. Use tools like tcpdump to capture unusual traffic patterns or netstat to observe network queue states.

Impact Analysis

This vulnerability can cause system instability or crashes due to excessive memory or CPU usage from the packet duplication loop. It may lead to denial-of-service conditions, disrupting network services or applications relying on the affected Linux kernel.

Compliance Impact

This vulnerability causes a denial-of-service condition by exhausting system resources through packet duplication in the Linux kernel's netem qdisc. It does not directly relate to data privacy or access controls required by standards like GDPR or HIPAA.

Mitigation Strategies

Apply the latest Linux kernel patches that address this issue. Update to a kernel version containing the fix for netem packet duplication. If immediate patching is not possible, disable netem qdisc or restrict its use to prevent packet duplication scenarios. Monitor network performance and kernel logs for signs of the vulnerability.

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