How to Fix CVE-2026-31430: Security vulnerability in Linux

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

What is CVE-2026-31430?

In the Linux kernel, the following vulnerability has been resolved: X.509: Fix out-of-bounds access when parsing extensions Leo reports an out-of-bounds access when parsing a certificate with empty Basic Constraints or Key Usage extension because the first byte of the extension is read before checking its length. Fix it. The bug can be triggered by an unprivileged user by submitting a specially crafted certificate to the kernel through the keyrings(7) API. Leo has demonstrated this with a proof-of-concept program responsibly disclosed off-list.

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 30eae2b037af54b24109dcaea21db46f6285c69b to <672b526def1f94c1be8eb11b885b803da0d8c2f1, 30eae2b037af54b24109dcaea21db46f6285c69b to <30ab358fad0c7daa1d282ec48089901b21b36a20, 30eae2b037af54b24109dcaea21db46f6285c69b to <206121294b9cf27f0589857f80d64f87e496ffb2, 30eae2b037af54b24109dcaea21db46f6285c69b to <7fb4dadc2734f4020d7543d688b8d49c8e569c61, 30eae2b037af54b24109dca...). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-31430

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 672b526def1f94c1be8eb11b885b803da0d8c2f1; Linux 30ab358fad0c7daa1d282ec48089901b21b36a20; Linux 206121294b9cf27f0589857f80d64f87e496ffb2; Linux 7fb4dadc2734f4020d7543d688b8d49c8e569c61 (and 1 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-2026-31430 affecting Linux kernel
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-31430-fix-$(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 672b526def1f94c1be8eb11b885b803da0d8c2f1; Linux 30ab358fad0c7daa1d282ec..."
    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-2026-31430 affecting Linux kernel
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-31430-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-2026-31430-$(date +%Y%m%d)"
mkdir -p "$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 672b526def1f94c1be8eb11b885b803da0d8c2f1; Linux 30ab358fad0c7daa1d282ec...)"
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 672b526def1f94c1be8eb11b885b803da0d8c2f1; Linux 30ab358fad0c7daa1d282ec48089901b21b36a20; Linux 206121294b9cf27f0589857f80d64f87e496ffb2; Linux 7fb4dadc2734f4020d7543d688b8d49c8e569c61 (and 1 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-2026-31690: firmware: thead: Fix buffer overflow and use standard endian macros in Linux — firmware: thead: Fix buffer overflow and use standard endian macros in Linux
• How to Fix CVE-2026-31516: xfrm: prevent policy_hthresh.work from racing with netns teardown in Linux — xfrm: prevent policy_hthresh.work from racing with netns teardown in Linux
• How to Fix CVE-2026-43208: Security Vulnerability in Linux , Security Vulnerability in Linux
• How to Fix CVE-2026-31439: dmaengine: xilinx: xdma: Fix regmap init error handling in Linux , dmaengine: xilinx: xdma: Fix regmap init error handling in Linux
• How to Fix CVE-2026-43307: Security Vulnerability in Linux , Security Vulnerability in Linux

Is CVE-2026-31430 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/672b526def1f94c1be8eb11b885b803da0d8c2f1
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31430
• https://git.kernel.org/stable/c/30ab358fad0c7daa1d282ec48089901b21b36a20
• https://git.kernel.org/stable/c/206121294b9cf27f0589857f80d64f87e496ffb2
• https://git.kernel.org/stable/c/7fb4dadc2734f4020d7543d688b8d49c8e569c61
• https://git.kernel.org/stable/c/d702c3408213bb12bd570bb97204d8340d141c51

*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.*