External risk intelligence

Linux Kernel Network Coalescing Shared Fragment Handling Flaw

CVE advisoryKnown Exploit

CVE-2026-46300

This vulnerability exists within the Linux kernel's socket buffer (skbuff) coalescing logic. It is a low-level memory management issue that requires an attacker to already have local access to the system to interact with specific kernel-level networking functions. It is not directly reachable or exploitable via the public internet.

Out-of-bounds Write

Linux Kernel

3.9 to 5.10.2575.11 to before 5.15.2085.16 to before 6.1.1746.2 to before 6.6.1416.7 to before 6.12.916.13 to before 6.18.336.19 to before 7.0.107.1

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 in the Linux kernel could allow an attacker with local access to potentially modify sensitive data. The issue stems from how the kernel handles network data fragments, where a marker indicating shared data could be lost, leading to unintended modifications.

Kernel flaw could allow data tampering.
Matters for systems managing network data integrity.
Confirm relevance and assess exposure.

Attack Path

How an attacker could exploit the issue

An attacker with local access to a Linux system can leverage a flaw in the kernel's networking stack. This flaw occurs when the system attempts to combine data fragments (coalescing) for network packets. Specifically, a shared fragment marker can be lost during this process, causing the kernel to incorrectly believe it can modify data in place, leading to the corruption of critical system components.

Local access is required.
Vulnerability triggered by packet coalescing.
Risk of privilege escalation to root.

Live Threat

Current exploitation, exposure, and threat context

When supported, this vulnerability could allow local attackers to corrupt network data by causing the kernel to incorrectly handle shared memory fragments during network packet coalescing. This could lead to the ESP input processing incorrectly decrypting data in place over shared fragments.

Network packet data.
Local access to network functions.
Potential data corruption or unauthorized access.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the Linux kernel's network stack requires initial local access, suggesting that system administrators, infrastructure teams, or platform teams are likely responsible for addressing it. The first step is to identify all Linux systems, confirm their exposure and criticality, and then prioritize remediation based on risk.

Identify and confirm affected Linux systems.
Verify system exposure and business criticality.
Plan risk-based remediation actions.

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 and its role in this vulnerability?

The Linux kernel is the foundational core of the operating system that manages hardware resources, including network communications. This issue involves the kernel's network stack, specifically how it efficiently merges, or "coalesces," data fragments within network packets to improve performance. The vulnerability occurs when the kernel loses track of whether these data fragments are shared, which is critical for maintaining memory integrity during network processing.

What does the CVE-2026-46300 vulnerability mean?

CVE-2026-46300 is a memory-related weakness classified as CWE-456 (Missing Initialization of a Variable). Essentially, when the kernel merges network packets, it fails to preserve a specific marker that identifies data as 'shared.' Because the kernel thinks the data is not shared, it may incorrectly allow processes to overwrite sensitive memory or modify data in place that should have been protected, leading to unintended system behavior.

How is this Linux kernel bug triggered?

An attacker needs local access to the system to interact with specific kernel-level networking functions. The bug is triggered during the skb_try_coalesce operation, which combines data fragments. Importantly, the vulnerability does not occur during tailroom copy operations, as those processes copy data into the kernel's linear memory rather than transferring existing frag descriptors, meaning those specific network paths remain unaffected by this marker loss.

Do I need to worry about this vulnerability?

According to Halo Surface Signal, this vulnerability is very unlikely to be exploited remotely because it requires local access to the system. It is not directly reachable from the public internet. You should primarily care if you manage high-security systems where local users or processes could potentially escalate privileges, though standard internet-facing services are not the primary vector for this specific kernel-level issue.

What are the first steps to address CVE-2026-46300?

Start by identifying all Linux systems in your environment that are running the affected kernel versions. Once identified, evaluate the criticality of these systems to determine your patching schedule. Since this is a kernel-level issue, coordinate with your infrastructure or platform teams to plan for the application of official vendor patches or security updates, ensuring you follow established maintenance windows for system reboots.

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.