External risk intelligence

Linux Kernel Frag Queue Use-After-Free Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-53175

This vulnerability resides in the Linux kernel's IP fragment reassembly logic. While it processes network traffic, the flaw requires triggering a specific race condition during network namespace teardown. It is reachable in networked environments, but public-facing exposure as a primary attack vector is not the standard deployment pattern.

Use After Free

Linux Kernel

6.18.3 to before 6.18.366.19.1 to before 7.0.136.12.936.197.1

Halo Surface Signal: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in the Linux kernel related to how network fragments are handled during network namespace teardown. This issue could lead to system instability or unauthorized access by exploiting a flaw in memory management when processing incomplete network data.

Kernel memory flaw affects network fragment handling.
Critical issue impacts system stability and potential access.
Confirm relevance and exposure within your environment.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted network packets that trigger a race condition within the Linux kernel's IP fragment reassembly process during network namespace teardown. This could lead to a use-after-free condition, allowing an attacker to potentially crash the system or execute arbitrary code.

Entry condition: Network exposure.
Trigger point: Network namespace teardown race condition.
Resulting risk: System crash or code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could affect network packet reassembly, potentially leading to system instability or unexpected behavior. The issue arises from a use-after-free condition in the Linux kernel's handling of fragmented network packets during network namespace teardown.

System memory could be corrupted.
A race condition during teardown could trigger the flaw.
System instability or crashes may occur.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the Linux kernel's IP fragment reassembly impacts network packet handling and could be triggered during network namespace teardown. Infrastructure or platform teams responsible for kernel maintenance and network services are likely to own this issue. The first practical step is to identify all systems running the affected kernel, confirm their network reachability and criticality, and then prioritize remediation efforts based on this exposure assessment.

Kernel and network teams own remediation.
Verify affected systems and network exposure.
Plan updates based on 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 fragment queue component?

The fragment queue component is part of the Linux kernel's networking stack, specifically responsible for reassembling fragmented IP packets. When data packets are too large for a network path, they are broken into fragments; the kernel tracks these pieces and stitches them back together. This mechanism is essential for IPv4, IPv6, and protocols like 6lowpan, ensuring that incomplete or stalled packet groups are managed properly until they can be successfully reassembled or discarded.

What is the nature of the vulnerability in CVE-2026-53175?

This is a Use-After-Free vulnerability. It occurs because the kernel's cleanup process incorrectly frees memory associated with network fragment queues while still keeping pointers to that memory. If a late-arriving packet attempts to access the queue after this cleanup has started but before the system fully realizes the queue is gone, it tries to use the deleted memory. This memory corruption can cause the system to crash or potentially allow unintended operations.

How does an attacker trigger this kernel flaw?

The bug is triggered by a race condition occurring exactly when a network namespace is being torn down. An attacker must send specific network packets to influence the fragment reassembly process during this precise closing window. Normal network traffic that does not happen to overlap with this teardown timing will not trigger the bug, as the flaw relies on the specific sequence of flushing fragments and resuming stalled queue operations.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal notes that while this flaw is reachable in networked environments, it is not a standard public-facing attack vector. Because the vulnerability requires a precise race condition during internal namespace teardown, the primary risk is limited to environments where network namespaces are frequently created and destroyed. You should assess whether your infrastructure relies heavily on these dynamic network configurations.

What should I do to address CVE-2026-53175?

Your first step is to identify all servers and container hosts running versions of the Linux kernel that handle IP fragment reassembly. Since this is a core kernel issue, remediation involves applying the official kernel patches provided by your distribution maintainer. Infrastructure teams should prioritize updating systems that are most critical or those that frequently cycle network namespaces, as these are the environments where the race condition is most likely to be encountered.

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.