How to Fix CVE-2026-31422: Security vulnerability in Linux

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

What is CVE-2026-31422?

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_flow: fix NULL pointer dereference on shared blocks flow_change() calls tcf_block_q() and dereferences q->handle to derive a default baseclass. Shared blocks leave block->q NULL, causing a NULL deref when a flow filter without a fully qualified baseclass is created on a shared block. Check tcf_block_shared() before accessing block->q and return -EINVAL for shared blocks. This avoids the null-deref shown below: ======================================================================= KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:flow_change (net/sched/cls_flow.c:508) Call Trace: tc_new_tfilter (net/sched/cls_api.c:2432) rtnetlink_rcv_msg (net/core/rtnetlink.c:6980) [...] =======================================================================

Am I affected?

Run the version check that matches your platform:

# Linux
dpkg -s linux-image-generic 2>/dev/null | grep -i version
rpm -q linux-image-generic 2>/dev/null
linux-image-generic --version 2>/dev/null

Compare what you see against the Affected row above (Linux 1abf272022cf1d18469405f47b4ec49c6a3125db to <57f94ac7e953eece5ed4819605a18f3cdfc63dcc, 1abf272022cf1d18469405f47b4ec49c6a3125db to <942813276edeb1741fa5b0a73471beb4e495fa08, 1abf272022cf1d18469405f47b4ec49c6a3125db to <cc707a4fd4c3b6ab2722e06bc359aa010e13d408, 1abf272022cf1d18469405f47b4ec49c6a3125db to <4a09f72007201c9f667dc47f64517ec23eea65e5, 1abf272022cf1d18469405f...). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-31422

The primary fix is to upgrade Linux to the patched build. Use the commands for your platform below; the patched versions listed in the vendor advisory are: Linux 57f94ac7e953eece5ed4819605a18f3cdfc63dcc; Linux 942813276edeb1741fa5b0a73471beb4e495fa08; Linux cc707a4fd4c3b6ab2722e06bc359aa010e13d408; Linux 4a09f72007201c9f667dc47f64517ec23eea65e5 (and 4 more SKUs, see vendor advisory).

Ubuntu / Debian

sudo apt-get update
sudo apt-get install --only-upgrade linux-image-generic
linux-image-generic --version 2>/dev/null || dpkg -s linux-image-generic | grep -i version

RHEL / CentOS / Rocky / AlmaLinux

sudo dnf upgrade --security linux-image-generic -y
rpm -q linux-image-generic

SUSE / openSUSE

sudo zypper patch --category security
rpm -q linux-image-generic

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2026-31422 affecting Linux kernel
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-31422-fix-$(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] Detecting installed version of Linux kernel"
    $pkg = winget list --id "Linux_kernel" 2>$null
    Write-Host $pkg

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

    Write-Host "[3/4] Applying upgrade to Linux 57f94ac7e953eece5ed4819605a18f3cdfc63dcc; Linux 942813276edeb1741fa5b0a..."
    winget upgrade --id "Linux_kernel" --silent --accept-source-agreements --accept-package-agreements
    # Fallback: Windows Update for OS-level fixes
    if ($LASTEXITCODE -ne 0) {
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verifying patched build"
    winget list --id "Linux_kernel"
    Write-Host "Fix 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-2026-31422 affecting Linux kernel
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-31422-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

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

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2026-31422-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/linux-image-generic /etc/linux-image-generic.d /etc/linux-image-generic.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Applying upgrade (target: Linux 57f94ac7e953eece5ed4819605a18f3cdfc63dcc; Linux 942813276edeb1741fa5b0a...)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y linux-image-generic
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y linux-image-generic
elif command -v yum >/dev/null; then
    yum update -y linux-image-generic
elif command -v zypper >/dev/null; then
    zypper --non-interactive patch --category security
fi

echo "[4/4] Verifying patched build"
if command -v dpkg >/dev/null; then
    dpkg -s linux-image-generic 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q linux-image-generic
fi
echo "Done. Restart any running daemons that loaded the old library."

If you can't patch immediately

If you cannot apply the patched version today, restrict exposure with one of the following runnable controls. None replace the patch.

Network restriction (Linux, nftables)

# Block inbound traffic to the affected service from untrusted networks
sudo nft add table inet filter
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }'
sudo nft 'add rule inet filter input tcp dport {443, 80} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Service-level fallback

# If the affected feature is optional, stop the service until the patch is applied
sudo systemctl stop linux-image-generic
sudo systemctl disable linux-image-generic

How to verify the fix worked

# Linux
linux-image-generic --version 2>/dev/null || dpkg -s linux-image-generic | grep -i version
rpm -q linux-image-generic 2>/dev/null || true

# Windows
winget list | findstr /I "linux-image-generic"
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above Linux 57f94ac7e953eece5ed4819605a18f3cdfc63dcc; Linux 942813276edeb1741fa5b0a73471beb4e495fa08; Linux cc707a4fd4c3b6ab2722e06bc359aa010e13d408; Linux 4a09f72007201c9f667dc47f64517ec23eea65e5 (and 4 more SKUs, see vendor advisory). Restart any services that loaded the old library (systemctl restart <service> on Linux, restart the Windows service or reboot when prompted). For network appliances, run show version on the device and confirm the build matches the patched release.

Frequently asked questions

Related fixes

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

• How to Fix CVE-2026-23194: Critical Vulnerability in Linux — Critical Vulnerability in Linux
• How to Fix CVE-2026-31596: ocfs2: handle invalid dinode in Linux — ocfs2: handle invalid dinode in Linux
• How to Fix CVE-2026-23218: Critical Vulnerability in Linux , Critical Vulnerability in Linux
• How to Fix CVE-2026-23111: Critical Vulnerability in Linux , Critical Vulnerability in Linux
• How to Fix CVE-2026-23132: Critical Vulnerability in Linux , Critical Vulnerability in Linux

Is CVE-2026-31422 actually being exploited?

According to the data sources above, no public confirmation of in-the-wild exploitation at this time. Either way, the fix is the same: apply the vendor patch.

Do I need to reboot after patching?

For OS or kernel updates, yes. For most userland packages a systemctl restart <service> is enough. Any process that loaded the old shared library keeps using it until restarted, so when in doubt, reboot.

What is the CVSS score?

The rating in the advisory. Refer to the vendor advisory for the exact vector string.

Where is the official advisory?

See the References section at the bottom of this page; the vendor's URL is the authoritative source for affected builds and patched versions.

References

• Official vendor advisory: https://git.kernel.org/stable/c/57f94ac7e953eece5ed4819605a18f3cdfc63dcc
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31422
• https://git.kernel.org/stable/c/942813276edeb1741fa5b0a73471beb4e495fa08
• https://git.kernel.org/stable/c/cc707a4fd4c3b6ab2722e06bc359aa010e13d408
• https://git.kernel.org/stable/c/4a09f72007201c9f667dc47f64517ec23eea65e5
• https://git.kernel.org/stable/c/9bf5fc36a43f7b8b5507c96e74fb81f1e8b4957e

*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.*