● Critical · CVSS 9.1

How to Fix CVE-2026-28386: Out-of-bounds Read in AES-CFB-128 on X86-64 with AVX-512 Support

Q: Is CVE-2026-28386 being actively exploited?

Not at the time of writing. It is not listed in CISA's Known Exploited Vulnerabilities catalog. That status can change, so monitor the vendor advisory and the KEV catalog if the system is exposed.

Q: How severe is CVE-2026-28386?

CVSS rates it 9.1 (Critical). Use that score to set your patch priority alongside the other items in your queue.

Q: Do I have to take OpenSSL offline to apply the patch?

It depends on the deployment. High-availability or clustered installs can usually patch one node at a time with no full outage. Standalone installs typically need a short restart. Always follow the vendor's documented upgrade steps.

Q: What if my vulnerability scanner still flags CVE-2026-28386 after I patch?

Re-run the scan after a service restart, then confirm the scanner's plugin set is up to date. Some scanners detect by banner version only and lag the official fix metadata by a release.

*By Sai Kiran Pandrala*

Last verified: 2026-05-25

⚡ At a glance


Severity	CVSS 9.1, Critical
Actively exploited?	No
Affected	OpenSSL (3.6.0 < 3.6.2)
Fixed in	3.6.2
Type (CWE)	CWE-125: Out-of-bounds Read

CVE-2026-28386 is a out-of-bounds read in aes-cfb-128 on x86-64 with avx-512 support in OpenSSL. The fix is to upgrade to 3.6.2 and apply the runnable commands below.

What is CVE-2026-28386?

Issue summary: Applications using AES-CFB128 encryption or decryption on

systems with AVX-512 and VAES support can trigger an out-of-bounds read

of up to 15 bytes when processing partial cipher blocks. Impact summary: This out-of-bounds read may trigger a crash which leads to

Denial of Service for an application if the input buffer ends at a memory

page boundary and the following page is unmapped. There is no information

disclosure as the over-read bytes are not written to output.

In practical terms, a successful attacker gets a denial-of-service condition that crashes or hangs the affected service. There is no confirmed in-the-wild exploitation listed in CISA's KEV catalog at the time of writing, but the CVSS rating still warrants prompt patching.

Am I affected?

You are affected if you run OpenSSL at a version listed in the Affected row above. Probe your installed build with the commands below.


openssl version

How to fix CVE-2026-28386

The primary fix is to upgrade to the patched build listed in the Fixed in row above (3.6.2). Pick the platform that matches your install and run the commands below.

Linux (Ubuntu/Debian)


sudo apt-get update
sudo apt-get install --only-upgrade openssl libssl1.1 libssl3
openssl version

Linux (RHEL/CentOS/Rocky)


sudo dnf upgrade --security openssl -y
rpm -q openssl

PowerShell script (Windows): detect, back up, upgrade, verify, log


# Run as Administrator
$ErrorActionPreference = 'Stop'
$log = "$env:ProgramData\OpenSSL-Patch-CVE-2026-28386.log"
function Write-Log($msg) { "$(Get-Date -Format s)  $msg" | Tee-Object -FilePath $log -Append }

Write-Log "Starting CVE-2026-28386 remediation for Openssl OpenSSL"

# 1. Detect: replace the path/version probe with one valid for your install
$installed = (Get-WmiObject -Class Win32_Product |
    Where-Object { $_.Name -like '*OpenSSL*' } |
    Select-Object -First 1 -ExpandProperty Version)
Write-Log "Detected version: $installed"

if (-not $installed) {
    Write-Log "Product not installed on this host; nothing to do."
    return
}
if ([version]$installed -ge [version]'3.6.2') {
    Write-Log "Already at fixed version $installed; no action needed."
    return
}

# 2. Backup configuration to a timestamped folder
$backup = "$env:ProgramData\OpenSSL-Backup-$(Get-Date -Format yyyyMMdd-HHmm)"
New-Item -ItemType Directory -Path $backup -Force | Out-Null
$src = "$env:ProgramFiles\Openssl\OpenSSL"
if (Test-Path $src) { Copy-Item -Path $src -Destination $backup -Recurse -Force }
Write-Log "Backed up config to $backup"

# 3. Apply the patched installer
$installer = "$env:TEMP\OpenSSL-3.6.2.msi"
if (-not (Test-Path $installer)) {
    throw "Patched installer not found at $installer. Stage it from your software repo first."
}
Start-Process msiexec.exe -ArgumentList "/i `"$installer`" /qn /norestart" -Wait
Write-Log "Installer finished"

# 4. Verify
$verify = (Get-WmiObject -Class Win32_Product |
    Where-Object { $_.Name -like '*OpenSSL*' } |
    Select-Object -First 1 -ExpandProperty Version)
if ([version]$verify -ge [version]'3.6.2') {
    Write-Log "SUCCESS: now at $verify (>= 3.6.2)"
} else {
    Write-Log "FAILURE: still at $verify after install"
    exit 1
}

Bash script (Linux): detect, back up, upgrade, verify, log


#!/usr/bin/env bash
set -euo pipefail
LOG=/var/log/openssl-patch-cve-2026-28386.log
log()  { echo "$(date -Iseconds)  $*" | tee -a "$LOG"; }

log "Starting CVE-2026-28386 remediation for Openssl OpenSSL"

# 1. Detect installed version (works for deb and rpm packages)
if command -v dpkg >/dev/null && dpkg -s openssl >/dev/null 2>&1; then
    CURRENT=$(dpkg-query -W -f='${Version}' openssl)
    PKG_MGR=apt
elif command -v rpm >/dev/null && rpm -q openssl >/dev/null 2>&1; then
    CURRENT=$(rpm -q --queryformat '%{VERSION}' openssl)
    PKG_MGR=dnf
else
    log "openssl not installed via apt or rpm; check your package manager or vendor instructions."
    exit 0
fi
log "Detected: openssl=$CURRENT (manager=$PKG_MGR)"

# 2. Backup config
BACKUP=/var/backups/openssl-$(date +%Y%m%d-%H%M)
mkdir -p "$BACKUP"
for d in /etc/openssl /etc/${pkg%%-*} ; do
    [ -d "$d" ] && cp -a "$d" "$BACKUP/" && log "Backed up $d to $BACKUP"
done

# 3. Upgrade
if [ "$PKG_MGR" = apt ]; then
    sudo apt-get update -y
    sudo apt-get install --only-upgrade -y openssl
else
    sudo dnf upgrade --security -y openssl
fi

# 4. Verify
if [ "$PKG_MGR" = apt ]; then
    NEW=$(dpkg-query -W -f='${Version}' openssl)
else
    NEW=$(rpm -q --queryformat '%{VERSION}' openssl)
fi
log "After upgrade: $NEW"
log "Done. Compare $NEW against 3.6.2 and restart the affected service if needed."

If you cannot patch immediately

These are runnable hardening commands. They reduce blast radius but they are not a replacement for the vendor patch.

Rate-limit and watchdog the affected service


sudo iptables -A INPUT -p tcp --dport 443 -m conntrack --ctstate NEW -m limit --limit 50/s -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -m conntrack --ctstate NEW -j DROP

How to verify the fix worked

Run the version probe again and confirm the running build matches the Fixed in row above.


openssl version

Expected output: OpenSSL 3.6.2 (or newer).

Re-run any vulnerability scanner you used previously and confirm the finding for CVE-2026-28386 has cleared. Sweep your logs for indicators of compromise listed in the vendor or CISA advisory, especially if the system was internet-reachable during the disclosure window.

This advisory covers multiple CVE IDs. The same patched build closes every entry below:

Frequently asked questions

Is CVE-2026-28386 being actively exploited?