External risk intelligence

Linux Kernel sch_fq_codel Packet Drop Issue Causes Memory Corruption.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-80630

This is a vulnerability in a Linux kernel network scheduler component (sch_fq_codel). It is an internal kernel-level memory management issue requiring local, privileged access or specific local traffic manipulation to trigger. It is not an internet-facing service or application endpoint.

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been resolved in the Linux kernel's network scheduling component. This issue could lead to instability or unexpected behavior when packets are dropped under specific traffic conditions. The main concern is confirming relevance and exposure within your environment.

Kernel component issue resolved.
Confirms relevance and potential exposure.
Assess if Linux kernel network scheduler is used.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by manipulating network traffic to trigger an issue within the Linux kernel's fq_codel component. This manipulation could lead to a memory access error, potentially causing a system crash. There is no information available on how an attacker might gain initial access to the system or the specific network traffic patterns required to trigger this condition.

Requires local network access or manipulation.
Triggered by specific network traffic conditions.
Risk of system crash or memory corruption.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could affect the stability of network traffic handling within the Linux kernel. Specifically, when certain conditions cause packet drops during a process called "peek," the kernel might mismanage its internal queues, leading to unexpected behavior and potential system crashes.

System stability.
Incorrect queue management.
System crashes or wild memory access.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability resides within the Linux kernel's network scheduler. Determining ownership and the first practical steps requires identifying which teams manage kernel-level network configurations and traffic shaping, confirming the exposure of affected systems, and then prioritizing remediation based on their criticality and reachability.

Kernel and network infrastructure teams own.
Verify affected systems and network exposure.
Plan remediation by system criticality.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Linux kernel component sch_fq_codel?

The sch_fq_codel component is a network scheduler within the Linux kernel. It is responsible for traffic shaping and queue management, helping to manage packet flow and reduce network latency by intelligently dropping packets when buffers become overloaded.

What is the nature of the vulnerability in CVE-2026-80630?

This vulnerability is a memory management flaw occurring during packet processing. It happens when the scheduler incorrectly reports queue status while inspecting packets, leading to improper memory access. This misalignment can cause the system to crash or experience memory corruption.

How is this CVE-2026-80630 vulnerability triggered?

The bug is triggered by specific, complex network traffic conditions that cause packet drops while the scheduler is performing a 'peek' operation. It is not triggered by standard, routine network traffic or normal system operation.

Is my system at risk according to Halo Surface Signal?

According to Halo Surface Signal, this vulnerability is very unlikely to be remotely exploitable. It affects an internal kernel-level component and generally requires local access or highly specific local traffic manipulation, rather than being an internet-facing service.

What should I do if my systems use this scheduler?

Work with your infrastructure or kernel management teams to identify systems actively using the sch_fq_codel scheduler. Prioritize these systems based on their role and criticality, and plan to apply the official kernel patches as part of your standard maintenance lifecycle.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.