CVSS 9.8 � CRITICAL Linux Kernel Cybersecurity

CVE-2026-98432: Critical Linux Kernel TCP Flaw � Impact, Affected Versions & Fix

A use-after-free vulnerability in Linux IPv4 TCP connection handling has raised security concerns for internet-facing servers. Here's what administrators need to know.

By Seminars Only October 30, 2026 Security Advisory

Quick Answer

CVE-2026-98432 is a Linux kernel IPv4 TCP use-after-free vulnerability caused by a race condition involving socket-option memory. The Linux kernel CVE authority rates it 9.8 Critical, while Red Hat assigns a product-specific score of 5.9 Moderate. The vulnerability can cause kernel crashes and denial of service, with more serious exploitation concerns in particular configurations. The upstream fix delays memory reclamation using kfree_rcu().

Fixed upstream kernel releases include 6.12.113, 6.18.56 and 7.2.10. Distribution-specific security updates must be verified separately.

CVE-2026-98432 Vulnerability Details

CVE ID	CVE-2026-98432
Component	Linux kernel IPv4 TCP networking
Vulnerability	Use-after-free race condition
CWE	CWE-825 (Red Hat classification)
Kernel CNA Score	CVSS 3.1: 9.8 Critical
Red Hat Score	CVSS 3.1: 5.9 Moderate
Attack Vector	Network
Privileges	None required
Published	October 15, 2026
Upstream Fix	RCU-delayed memory freeing

What Causes CVE-2026-98432?

The flaw occurs during IPv4 TCP connection setup. The kernel's tcp_v4_syn_recv_sock() function transfers ownership of IP options from a pending connection request to a child socket without copying them.

At the same time, another CPU may process a retransmitted SYN packet for the same request. That processing can read the original options while preparing a SYNACK response.

If the child socket is destroyed and the option memory is freed before the other CPU finishes reading it, the second operation can reference memory that is no longer valid.

Simplified Vulnerability Sequence

A client initiates an IPv4 TCP connection.
The kernel creates a request socket containing IP options.
One CPU processes the connection and transfers option ownership.
Another CPU processes a retransmitted SYN.
The child socket may be destroyed, freeing option memory.
The second CPU may still access that freed memory.
The result is a use-after-free condition.

A related issue occurs during TCP request socket migration, including paths associated with net.ipv4.tcp_migrate_req and certain reuseport BPF programs.

The upstream correction replaces immediate freeing with kfree_rcu() in affected cleanup paths, allowing existing RCU readers to complete before memory is reclaimed.

Why Do CVSS Scores Differ?

The Linux kernel CVE authority assigns a critical score of 9.8, reflecting a network-accessible vulnerability with potential confidentiality, integrity, and availability consequences.

Red Hat assigns a lower score of 5.9 for its products because the race is difficult to trigger reliably, and Red Hat's assessment identifies denial of service as the most likely practical outcome.

Linux Kernel CNA

9.8

Critical

Red Hat

5.9

Moderate

CVSS scores are risk indicators, not proof of successful exploitation. Administrators should consider the vendor assessment, kernel build, exposed services, and actual network configuration.

Affected and Fixed Linux Kernel Versions

The official kernel CVE announcement identifies the vulnerability as introduced in Linux 4.4. It documents the following upstream fixed releases.

Kernel Branch	Fixed Release
6.12	6.12.113
6.18	6.18.56
7.2	7.2.10
7.3 development	7.3-rc7

Important: Distribution vendors often backport kernel security patches. A kernel with an older version number may already contain a fix. Conversely, updating to a package that does not include the correction will not resolve the vulnerability.

Distribution-Specific Status

Red Hat identifies RHEL 8, 9, and 10, along with related kernel products, as affected. RHEL 7 is listed as not affected. Its published advisory describes fixes as deferred.

Ubuntu, Debian, Oracle Linux, Amazon Linux, and SUSE users should consult their respective CVE trackers. Patch availability varies by release and can change after this article is published.

What Is the Security Impact?

Kernel Crash

A successful trigger may cause a kernel crash and interrupt hosted applications or services.

Memory Safety Risk

Use-after-free flaws can lead to memory corruption. Exploitability depends on the system and triggering conditions.

Remote code execution has also been discussed in recent security research involving particular Linux configurations. That does not establish that every affected Linux server can be remotely compromised. Operators should not dismiss the issue solely because one vendor assigns a moderate severity rating.

How to Fix CVE-2026-98432

Step 1: Check Your Kernel

uname -r
cat /etc/os-release

Identify the running kernel and distribution. Record these details before applying updates.

Step 2: Check Your Vendor Advisory

Search your distribution's security tracker for CVE-2026-98432. Confirm whether your specific release is affected and whether a fixed kernel package has been published.

Step 3: Install an Available Fixed Kernel

Ubuntu / Debian:

sudo apt update
sudo apt upgrade

RHEL / Fedora:

sudo dnf upgrade

These commands install available updates. They do not guarantee that this particular CVE has been fixed. Always compare the installed kernel package against the vendor's security advisory.

Step 4: Reboot When Required

sudo reboot

Schedule a maintenance window for production servers. Ensure redundancy, backups, and recovery procedures are available before restarting critical systems.

Step 5: Verify the Active Kernel

uname -r

Confirm that the system is running the fixed kernel package identified by your vendor. Merely installing a new package without rebooting may leave the old kernel active.

What If No Security Patch Is Available?

If a vendor has not yet released a fixed kernel, reduce unnecessary network exposure and monitor affected systems. These measures are not substitutes for a verified security patch.

Restrict unnecessary public-facing TCP services.
Use network segmentation and firewall policies.
Monitor unusual kernel crashes and networking errors.
Review the use of MPTCP and request socket migration where applicable.
Follow official distribution security advisories.
Prepare a tested kernel update and rollback procedure.

Red Hat currently does not identify a broadly applicable supported mitigation for its affected products. Avoid assuming that disabling one kernel option completely removes exposure.

How to Monitor Linux Kernel Errors

Review kernel warnings from the current boot:

sudo journalctl -k -b -p warning

Inspect recent kernel messages:

sudo dmesg -T

These commands can reveal kernel warnings and crashes, but they cannot conclusively establish exploitation of CVE-2026-98432.

Frequently Asked Questions

Is CVE-2026-98432 critical?

The Linux kernel CVE authority assigns a CVSS score of 9.8 Critical. Vendor-specific ratings can differ, including Red Hat's 5.9 Moderate assessment.

Can CVE-2026-98432 be exploited remotely?

The vulnerability is network-accessible. Successful exploitation depends on timing and configuration. Research has raised concerns about more serious outcomes on certain systems.

Which Linux kernel versions contain the fix?

The kernel CVE announcement identifies upstream fixes in 6.12.113, 6.18.56, 7.2.10 and 7.3-rc7. Distribution backports may provide equivalent protection.

Is Ubuntu affected?

Potentially affected Ubuntu releases must be checked through Canonical's CVE tracker. Package status is release-specific.

Does this affect IPv6?

The main IPv4 issue does not apply identically to IPv6. The upstream advisory notes a separate IPv6 migration-related issue involving CALIPSO options.

Does updating a Docker container fix it?

Not by itself. Containers generally share the host kernel, so kernel remediation must be performed on the underlying host.

Official Sources and References

TL;DR � CVE-2026-98432

Linux kernel IPv4 TCP use-after-free vulnerability.
Published October 15, 2026.
Kernel CNA severity: CVSS 9.8 Critical.
Red Hat product-specific severity: CVSS 5.9 Moderate.
Can cause kernel crashes and denial of service.
Fixed in multiple upstream stable kernel releases.
Check your Linux distribution for a verified fixed package.
Install the fix and reboot when required.

Editorial note: This article summarizes public Linux kernel and distribution security advisories as of October 30, 2026. Vulnerability assessments and patch availability may change. Always confirm current information using official vendor sources.