⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Not verified

How to Fix CVE-2026-31423: Security vulnerability in Linux

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

⚡ At a glance
SeverityNot verified, see advisory
Actively exploited?No public listing in CISA KEV
AffectedLinux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <ad8e8fec40290a8c8cf145c0deaadf76f80c5163, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <25b6821884713a31e2b49fb67b0ebd765b33e0a9, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <c56f78614e7781aaceca9bd3cb2128bf7d45c3bd, 1da177e4c3f41524e886b7f...
Fixed inLinux ad8e8fec40290a8c8cf145c0deaadf76f80c5163; Linux ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f; Linux 25b6821884713a31e2b49fb67b0ebd765b33e0a9; Linux c56f78614e7781aaceca9bd3cb2128bf7d45c3bd (and 4 more SKUs, see vendor advisory)
Type (CWE)Not verified, see official advisory

What is CVE-2026-31423?

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_hfsc: fix divide-by-zero in rtsc_min() m2sm() converts a u32 slope to a u64 scaled value. For large inputs (e.g. m1=4000000000), the result can reach 2^32. rtsc_min() stores the difference of two such u64 values in a u32 variable dsm and uses it as a divisor.

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 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <ad8e8fec40290a8c8cf145c0deaadf76f80c5163, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <25b6821884713a31e2b49fb67b0ebd765b33e0a9, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to <c56f78614e7781aaceca9bd3cb2128bf7d45c3bd, 1da177e4c3f41524e886b7f...). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-31423

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 ad8e8fec40290a8c8cf145c0deaadf76f80c5163; Linux ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f; Linux 25b6821884713a31e2b49fb67b0ebd765b33e0a9; Linux c56f78614e7781aaceca9bd3cb2128bf7d45c3bd (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

Docker / Kubernetes


# Vendor advisory: https://git.kernel.org/stable/c/ad8e8fec40290a8c8cf145c0deaadf76f80c5163
# Pull the patched image
docker pull linuxkernel:latest
# Or pin to the patched tag from the vendor's registry

# Rolling update in Kubernetes
kubectl set image deployment/linuxkernel linuxkernel=linuxkernel:<patched-tag>
kubectl rollout status deployment/linuxkernel

Complete PowerShell remediation script (Windows)


# Fix script for CVE-2026-31423 affecting Linux kernel
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-31423-fix-$(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 ad8e8fec40290a8c8cf145c0deaadf76f80c5163; Linux ab1ff5890c7354afc7be565..."
    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-2026-31423 affecting Linux kernel
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-31423-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-2026-31423-$(date +%Y%m%d)"
mkdir -p "$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 ad8e8fec40290a8c8cf145c0deaadf76f80c5163; Linux ab1ff5890c7354afc7be565...)"
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 ad8e8fec40290a8c8cf145c0deaadf76f80c5163; Linux ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f; Linux 25b6821884713a31e2b49fb67b0ebd765b33e0a9; Linux c56f78614e7781aaceca9bd3cb2128bf7d45c3bd (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

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

Is CVE-2026-31423 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

*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.*