CVE-2026-98432 Fix: Quick Linux Mitigation and Patch Guide

Key Takeaways

• The permanent fix is a patched kernel. Temporary firewall rules reduce exposure but do not eliminate the vulnerability.
• Check your exact distribution and kernel package. An update command succeeding does not prove this CVE is fixed.
• Apply compatible mitigations while waiting for patches. Red Hat publishes an IPv4-options filtering rule for this purpose.

Updated November 2, 2026.

1. Check the Running System

CVE-2026-98432 affects Linux IPv4 TCP processing. AWS reports demonstrated unauthenticated remote code execution against systems with an MPTCP listener.

Run these read-only checks on the affected host:

cat /etc/os-release
uname -r
sysctl net.mptcp.enabled
sysctl net.ipv4.tcp_migrate_req

Record the original settings before changing them. A missing sysctl key does not establish that the kernel is patched.

2. Apply the Temporary nftables Rule

The Red Hat mitigation filters TCP packets carrying IPv4 options. Ordinary TCP options, including MSS and window scaling, remain permitted. Test compatibility before production deployment; syntax validation alone does not test application behavior.

With nftables installed, create the rule file:

cat > cve-2026-98432.nft <<'EOF'
table inet cve_2026_98432 {
    chain input {
        type filter hook input priority -310; policy accept;
        ip protocol tcp ip hdrlength > 5 counter drop
    }
}
EOF

Validate, then apply only if validation succeeds:

sudo nft --check --file cve-2026-98432.nft && sudo nft --file cve-2026-98432.nft
sudo nft list table inet cve_2026_98432

Container caveat: this rule uses the host's input hook. Traffic forwarded to containers can take a different path; assess that path separately. The nftables hook documentation explains this distinction.

3. Disable Unneeded MPTCP and Request Migration

If these settings exist and the workload does not require them:

sudo sysctl -w net.mptcp.enabled=0
sudo sysctl -w net.ipv4.tcp_migrate_req=0

Understand the limits:

• MPTCP: the setting controls creation of new MPTCP sockets in the current network namespace. Do not assume existing listeners have closed; review affected services.
• Request migration: the default is already 0. BPF-directed migration is another path, so this setting is not comprehensive protection.
• Persistence: sysctl -w changes runtime values. Configure required boot-time settings separately; also integrate the nftables rule with the existing firewall configuration if it must survive reboot.

4. Install the Patch and Verify It

As checked on November 2:

• Ubuntu: the CVE tracker still lists the standard linux packages for 22.04, 24.04 and 26.04 as vulnerable, with fixes in progress. A planned version is not a released fix. Check your exact kernel flavor.
• RHEL: consult the package and errata tracker for an available fix in your update stream.
• Amazon Linux: AWS lists patched packages and requires a reboot. Choose the command matching your OS. Amazon Linux 2023 requires release 2023.12.20261102 or later.

For Amazon Linux 2:

sudo yum update kernel

For Amazon Linux 2023:

sudo dnf update kernel --releasever=latest

After confirming the fixed package installed, reboot during a maintenance window:

sudo reboot

After reconnecting, check the active kernel and compare it with the vendor's fixed package:

uname -r

Installing a kernel does not activate it. Retain mitigations until the running kernel is confirmed fixed. Then remove this temporary table:

sudo nft delete table inet cve_2026_98432

Remove any corresponding persistent firewall entry and review temporary sysctl changes against their recorded original values.

Conclusion

Check exposure, apply compatible temporary controls, and boot a vendor-confirmed fixed kernel. Start with your distribution's advisory and verify the running kernel before marking CVE-2026-98432 resolved.