How to Fix CVE-2026-23231: Security vulnerability in Linux

By Sai Kiran Pandrala. Last verified: 2026-05-25.

CVE-2026-23231 is a security vulnerability in Linux Linux. The fix is to upgrade to Linux 0; Linux 6.1.165; Linux 6.12.75; Linux 6.18.14; Linux 6.19.4; Linux 6.6.128.

What is CVE-2026-23231?

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: fix use-after-free in nf_tables_addchain()

nf_tables_addchain() publishes the chain to table->chains via

list_add_tail_rcu() (in nft_chain_add()) before registering hooks.

If nf_tables_register_hook() then fails, the error path calls

nft_chain_del() (list_del_rcu()) followed by nf_tables_chain_destroy()

with no RCU grace period in between.

This creates two use-after-free conditions:

1) Control-plane: nf_tables_dump_chains() traverses table->chains

under rcu_read_lock(). A concurrent dump can still be walking

the chain when the error path frees it.

2) Packet path: for NFPROTO_INET, nf_register_net_hook() briefly

installs the IPv4 hook before IPv6 registration fails. Packets

entering nft_do_chain() via the transient IPv4 hook can still be

dereferencing chain->blob_gen_X when the error path frees the

chain.

Add synchronize_rcu() between nft_chain_del() and the chain destroy

so that all RCU readers -- both dump threads and in-flight packet

evaluation -- have finished before the chain is freed. The CVSS base score is 7.8 (High), which puts this in the upper risk band and warrants a fast patch cycle. The official advisory is at https://git.kernel.org/stable/c/2a6586ecfa4ce1413daaafee250d2590e05f1a33.

Am I affected?

Check the version of Linux you are running and compare it against the Affected row above (Linux 91c7b38dc9f0de4f7f444b796d14476bc12df7bc to <2a6586ecfa4ce1413daaafee250d2590e05f1a33; Linux 91c7b38dc9f0de4f7f444b796d14476bc12df7bc to <7017745068a9068904e1e7a1b170a5785647cc81; Linux 91c7b38dc9f0de4f7f444b796d14476bc12df7bc to <f3fe58ce37926a10115ede527d59b91bcc05400a; Linux 91c7b38dc9f0de4f7f444b796d14476bc12df7bc to <dbd0af8083dd201f07c49110b2ee93710abdff28; Linux 91c7b38dc9f0de4f7f444b796d14476bc12df7bc to <2f9a4ffeb763aec822f8ff3d1e82202d27d46d4b; Linux 91c7b38dc9f0de4f7f444b796d14476bc12df7bc to <71e99ee20fc3f662555118cf1159443250647533). If your build sits inside the affected range, you must patch.

Run the version check that fits your platform:

# Linux package check
dpkg -s linux 2>/dev/null | grep -i ^Version
rpm -q linux 2>/dev/null
command -v linux >/dev/null && linux --version 2>/dev/null

# Windows (PowerShell)
Get-Package -Name "*Linux*" -ErrorAction SilentlyContinue | Select-Object Name, Version
winget list --name "Linux" 2>$null

How to fix CVE-2026-23231

Upgrade Linux to a patched build: Linux 0; Linux 6.1.165; Linux 6.12.75; Linux 6.18.14; Linux 6.19.4; Linux 6.6.128. The vendor advisory is the source of truth for the exact fixed version.

Ubuntu / Debian

sudo apt-get update
sudo apt-get install --only-upgrade linux
dpkg -s linux | grep -i ^Version

RHEL / CentOS / Rocky / AlmaLinux

sudo dnf upgrade --refresh linux -y
# or for older releases:
sudo yum update linux -y
rpm -q linux

SUSE / openSUSE

sudo zypper refresh
sudo zypper update linux
rpm -q linux

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2026-23231 affecting Linux
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-23231-fix-$(Get-Date -Format yyyyMMdd-HHmmss).log"
New-Item -ItemType Directory -Force (Split-Path $LogPath) | Out-Null
Start-Transcript -Path $LogPath -Append

try {
    Write-Host "[1/4] Detect installed version"
    $pkg = Get-Package -Name "*Linux*" -ErrorAction SilentlyContinue
    if ($pkg) { $pkg | Format-Table Name, Version }
    else { Write-Host "Not detected via Get-Package; try winget list" }

    Write-Host "[2/4] Backup configuration"
    $backup = "C:\Backup\linux-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\Linux" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Apply the upgrade to Linux 0; Linux 6.1.165; Linux 6.12.75; Linux 6.18.14; Linux 6.19.4; Linux 6.6.128"
    winget upgrade --name "Linux" --silent --accept-source-agreements --accept-package-agreements
    if ($LASTEXITCODE -ne 0) {
        # Fallback: pull latest via OS update channel
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verify the patched build"
    winget list --name "Linux"
    Write-Host "Patch applied. Reboot if prompted."
    exit 0
} catch {
    Write-Error "Patch failed: $_"
    exit 1
} finally {
    Stop-Transcript
}

Complete Bash remediation script (Linux)

#!/usr/bin/env bash
# Fix script for CVE-2026-23231 affecting Linux
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-23231-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Detect installed version"
if command -v dpkg >/dev/null; then
    dpkg -s linux 2>/dev/null | grep -i ^Version || echo "linux not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q linux || echo "linux not installed via rpm"
fi

echo "[2/4] Backup configuration"
BACKUP="/root/backup-cve-2026-23231-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/linux /etc/linux.d /etc/linux.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Apply the upgrade (target: Linux 0; Linux 6.1.165; Linux 6.12.75; Linux 6.18.14; Linux 6.19.4; Linux 6.6.128)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y linux
elif command -v dnf >/dev/null; then
    dnf upgrade --refresh -y linux
elif command -v yum >/dev/null; then
    yum update -y linux
elif command -v zypper >/dev/null; then
    zypper --non-interactive update linux
fi

echo "[4/4] Verify the patched build"
if command -v dpkg >/dev/null; then
    dpkg -s linux 2>/dev/null | grep -i ^Version
elif command -v rpm >/dev/null; then
    rpm -q linux
fi
echo "Done. Restart any service that loaded the old library."

If you can't patch immediately

Apply at least one of the following inline controls until you can deploy the patched build. None replace the upgrade.

Restrict exposure with nftables (Linux)

# Allow only trusted CIDR to reach the affected service ports
sudo nft add table inet filter 2>/dev/null || true
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }' 2>/dev/null || true
sudo nft 'add rule inet filter input tcp dport {80, 443} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Block at the host firewall (Windows)

New-NetFirewallRule -DisplayName "Block-CVE-2026-23231" -Direction Inbound -Action Block -Protocol TCP -LocalPort 80,443 -RemoteAddress Any -Enabled True
Get-NetFirewallRule -DisplayName "Block-CVE-2026-23231"

Disable the affected service (Linux)

sudo systemctl stop linux 2>/dev/null || true
sudo systemctl disable linux 2>/dev/null || true

If the vendor advisory lists an official workaround, prefer that wording verbatim. If no workaround is published, the only safe remediation is the patch.

How to verify the fix worked

After upgrading, confirm the installed version matches the patched build and that no old library is still loaded by a long-running process.

# Linux
dpkg -s linux 2>/dev/null | grep -i ^Version
rpm -q linux 2>/dev/null || true
# Pid map check for old library handles
sudo lsof +c0 2>/dev/null | grep -i "DEL.*lib" || true

# Windows
Get-Package -Name "*Linux*" | Select-Object Name, Version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above Linux 0; Linux 6.1.165; Linux 6.12.75; Linux 6.18.14; Linux 6.19.4; Linux 6.6.128. Restart the affected service (systemctl restart <service> on Linux, or restart the Windows service) so it loads the patched binary.

Frequently asked questions

Related fixes

Other vulnerabilities in the same area that are worth patching alongside this one:

• How to Fix CVE-2026-43457: Security Vulnerability in Linux — Security Vulnerability in Linux
• How to Fix CVE-2026-31429: Security vulnerability in Linux — Security vulnerability in Linux
• How to Fix CVE-2026-31461: drm/amd/display: Fix drm_edid leak in Linux , drm/amd/display: Fix drm_edid leak in Linux
• How to Fix CVE-2026-23021: Critical Vulnerability in Linux , Critical Vulnerability in Linux
• How to Fix CVE-2026-43135: Security Vulnerability in Linux , Security Vulnerability in Linux

Is CVE-2026-23231 actively exploited?

There is no public confirmation of exploitation in the wild listed in CISA KEV at the time of this writing. Patch anyway. Public exploits commonly follow disclosure within weeks.

Do I need to reboot after patching CVE-2026-23231?

For kernel and OS-level updates, yes. For most userland packages a systemctl restart <service> is enough on Linux, and restarting the Windows service or app on Windows. Any process that loaded the old library keeps using it until restarted.

What is the CVSS score for CVE-2026-23231?

7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Where is the official advisory for CVE-2026-23231?

The vendor advisory is at https://git.kernel.org/stable/c/2a6586ecfa4ce1413daaafee250d2590e05f1a33. The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-23231.

References

• Official vendor advisory: https://git.kernel.org/stable/c/2a6586ecfa4ce1413daaafee250d2590e05f1a33
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23231
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Additional reference: https://git.kernel.org/stable/c/7017745068a9068904e1e7a1b170a5785647cc81
• Additional reference: https://git.kernel.org/stable/c/f3fe58ce37926a10115ede527d59b91bcc05400a
• Additional reference: https://git.kernel.org/stable/c/dbd0af8083dd201f07c49110b2ee93710abdff28

*Written by Sai Kiran Pandrala. Assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.*