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

Reduce CVE-2026-98432 exposure with nftables and targeted sysctl settings, then install and verify a patched Linux kernel.

Canonical URL: https://aiidelist.com/blog/cve-2026-98432-linux-fix

Language: en

Published: 2026-11-02

Updated: 2026-11-02

## 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:

```bash
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](https://access.redhat.com/security/vulnerabilities/RHSB-2026-016) 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:

```bash
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:

```bash
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](https://wiki.nftables.org/wiki-nftables/index.php/Netfilter_hooks) explains this distinction. 

## 3. Disable Unneeded MPTCP and Request Migration

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

```bash
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](https://ubuntu.com/security/CVE-2026-98432) 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](https://access.redhat.com/security/cve/cve-2026-98432) 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:

```bash
sudo yum update kernel
```

For Amazon Linux 2023:

```bash
sudo dnf update kernel --releasever=latest
```

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

```bash
sudo reboot
```

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

```bash
uname -r
```

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

```bash
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.