CVE-2026-98013
Received Received - Intake

Denial of Service in Linux Kernel FQ_PIE Scheduler

Publication date: 2026-09-25

Last updated on: 2026-09-25

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: fq_pie: clamp quantum in change path fq_pie_change() accepts any quantum value from userspace, including 1. With a crafted size table qdisc_pkt_len reaches ~2 GiB, so quantum=1 makes the deficit-refill loop spin ~2^31 times under the qdisc lock (a soft lockup / denial of service). Add max(256U, ...) matching fq_codel_change(). Conditions to recreate the bug: CONFIG_NET_SCH_FQ_PIE=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices). tc qdisc add dev dummy0 root fq_pie tc qdisc change dev dummy0 root fq_pie quantum 1 stab data 32768 size_log 15 cell_log 0

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Meta Information

Published
2026-09-25
Last Modified
2026-09-25
Generated
2026-09-25
AI Q&A
2026-09-25
EPSS Evaluated
N/A
NVD
CVE-2026-98013
EUVD
EUVD-2026-86666

Affected Vendors & Products

Currently, no data is known.

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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 is a denial of service vulnerability in the Linux kernel's fq_pie traffic control module. It occurs when an attacker with CAP_NET_ADMIN privileges sets the quantum parameter to 1, causing a soft lockup by forcing a loop to spin excessively (~2^31 times) while holding a lock.

Detection Guidance

To detect this vulnerability, check if CONFIG_NET_SCH_FQ_PIE is enabled in your kernel configuration. If enabled, attempt to reproduce the issue by running the provided commands under CAP_NET_ADMIN privileges. Monitor for soft lockups or system unresponsiveness.

Impact Analysis

If exploited, this vulnerability can cause system unresponsiveness or crashes due to CPU exhaustion from the spinning loop. It requires local access with specific privileges but can disrupt network traffic management on affected systems.

Mitigation Strategies

Apply the kernel patch that clamps the quantum value to a minimum of 256. Alternatively, disable the fq_pie qdisc module if not required. Ensure your kernel is updated to a version containing the fix.

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