● High · CVSS 7.4

How to Fix CVE-2026-20033: Buffer access with incorrect length value in Cisco NX-OS System Software in ACI Mode

Q: What is the CVSS score for CVE-2026-20033?

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

Q: Where is the official advisory for CVE-2026-20033?

The vendor advisory is at [https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-cpdos-qLsv6pFD](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-cpdos-qLsv6pFD). The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-20033.

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

CVE-2026-20033 is a buffer access with incorrect length value in Cisco Cisco NX-OS System Software in ACI Mode. The fix is to apply the vendor patch noted below.

⚡ At a glance


Severity	7.4 (High)
Actively exploited?	No public listing in CISA KEV
Affected	Cisco NX-OS System Software in ACI Mode 15.2(1g); Cisco NX-OS System Software in ACI Mode 15.2(2e); Cisco NX-OS System Software in ACI Mode 15.2(2f); Cisco NX-OS System Software in ACI Mode 15.2(2g); Cisco NX-OS System Software in ACI Mode 15.2(2h); Cisco NX-OS System Software in ACI Mode 15.2(3f)
Fixed in	See vendor advisory
Type (CWE)	CWE-805: Buffer Access with Incorrect Length Value

What is CVE-2026-20033?

A vulnerability in Cisco Nexus 9000 Series Fabric Switches in ACI mode could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device.

This vulnerability is due to insufficient validation when processing specific Ethernet frames. An attacker could exploit this vulnerability by sending a crafted Ethernet frame to the management interface of an affected device. A successful exploit could allow the attacker to cause the device to reload unexpectedly, resulting in a DoS condition.

Note: Only the out-of-band (OOB) management interface is affected. The CVSS base score is 7.4 (High), which puts this in the upper risk band and warrants a fast patch cycle. The official advisory is at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-cpdos-qLsv6pFD.

Am I affected?

Check the version of Cisco NX-OS System Software in ACI Mode you are running and compare it against the Affected row above (Cisco NX-OS System Software in ACI Mode 15.2(1g); Cisco NX-OS System Software in ACI Mode 15.2(2e); Cisco NX-OS System Software in ACI Mode 15.2(2f); Cisco NX-OS System Software in ACI Mode 15.2(2g); Cisco NX-OS System Software in ACI Mode 15.2(2h); Cisco NX-OS System Software in ACI Mode 15.2(3f)). If your build sits inside the affected range, you must patch.

Run the version check that fits your platform:


# Linux package check
dpkg -s cisco-nx-os-system-software-in-aci-mode 2>/dev/null | grep -i ^Version
rpm -q cisco-nx-os-system-software-in-aci-mode 2>/dev/null
command -v cisco-nx-os-system-software-in-aci-mode >/dev/null && cisco-nx-os-system-software-in-aci-mode --version 2>/dev/null


# Windows (PowerShell)
Get-Package -Name "*Cisco NX-OS System Software in ACI Mode*" -ErrorAction SilentlyContinue | Select-Object Name, Version
winget list --name "Cisco NX-OS System Software in ACI Mode" 2>$null

How to fix CVE-2026-20033

Upgrade Cisco NX-OS System Software in ACI Mode to a patched build: See vendor advisory. 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 cisco-nx-os-system-software-in-aci-mode
dpkg -s cisco-nx-os-system-software-in-aci-mode | grep -i ^Version

RHEL / CentOS / Rocky / AlmaLinux


sudo dnf upgrade --refresh cisco-nx-os-system-software-in-aci-mode -y
# or for older releases:
sudo yum update cisco-nx-os-system-software-in-aci-mode -y
rpm -q cisco-nx-os-system-software-in-aci-mode

SUSE / openSUSE


sudo zypper refresh
sudo zypper update cisco-nx-os-system-software-in-aci-mode
rpm -q cisco-nx-os-system-software-in-aci-mode

Complete PowerShell remediation script (Windows)


# Fix script for CVE-2026-20033 affecting Cisco NX-OS System Software in ACI Mode
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-20033-fix-$(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"
    $pkg = Get-Package -Name "*Cisco NX-OS System Software in ACI Mode*" -ErrorAction SilentlyContinue
    if ($pkg) { $pkg | Format-Table Name, Version }
    else { Write-Host "Not detected via Get-Package; try winget list" }

    Write-Host "[2/4] Backup configuration"
    $backup = "C:\Backup\cisco-nx-os-system-software-in-aci-mode-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\Cisco NX-OS System Software in ACI Mode" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Apply the upgrade to See vendor advisory"
    winget upgrade --name "Cisco NX-OS System Software in ACI Mode" --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 "Cisco NX-OS System Software in ACI Mode"
    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-2026-20033 affecting Cisco NX-OS System Software in ACI Mode
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-20033-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 cisco-nx-os-system-software-in-aci-mode 2>/dev/null | grep -i ^Version || echo "cisco-nx-os-system-software-in-aci-mode not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q cisco-nx-os-system-software-in-aci-mode || echo "cisco-nx-os-system-software-in-aci-mode not installed via rpm"
fi

echo "[2/4] Backup configuration"
BACKUP="/root/backup-cve-2026-20033-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/cisco-nx-os-system-software-in-aci-mode /etc/cisco-nx-os-system-software-in-aci-mode.d /etc/cisco-nx-os-system-software-in-aci-mode.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Apply the upgrade (target: See vendor advisory)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y cisco-nx-os-system-software-in-aci-mode
elif command -v dnf >/dev/null; then
    dnf upgrade --refresh -y cisco-nx-os-system-software-in-aci-mode
elif command -v yum >/dev/null; then
    yum update -y cisco-nx-os-system-software-in-aci-mode
elif command -v zypper >/dev/null; then
    zypper --non-interactive update cisco-nx-os-system-software-in-aci-mode
fi

echo "[4/4] Verify the patched build"
if command -v dpkg >/dev/null; then
    dpkg -s cisco-nx-os-system-software-in-aci-mode 2>/dev/null | grep -i ^Version
elif command -v rpm >/dev/null; then
    rpm -q cisco-nx-os-system-software-in-aci-mode
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-2026-20033" -Direction Inbound -Action Block -Protocol TCP -LocalPort 80,443 -RemoteAddress Any -Enabled True
Get-NetFirewallRule -DisplayName "Block-CVE-2026-20033"

Disable the affected service (Linux)


sudo systemctl stop cisco-nx-os-system-software-in-aci-mode 2>/dev/null || true
sudo systemctl disable cisco-nx-os-system-software-in-aci-mode 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 cisco-nx-os-system-software-in-aci-mode 2>/dev/null | grep -i ^Version
rpm -q cisco-nx-os-system-software-in-aci-mode 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 "*Cisco NX-OS System Software in ACI Mode*" | Select-Object Name, Version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above See vendor advisory. Restart the affected service (systemctl restart <service> on Linux, or restart the Windows service) so it loads the patched binary.

Frequently asked questions

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

How to Fix CVE-2026-20070: Improper neutralization of script-related html tags in a web page (basic xss) in. — Improper neutralization of script-related html tags in a web page (basic xss) in.
How to Fix CVE-2026-20092: Arbitrary File Read in Cisco Intersight Virtual Appliance — Arbitrary File Read in Cisco Intersight Virtual Appliance
How to Fix CVE-2026-20102: Cross-site scripting in Cisco Secure Firewall Adaptive Security Appliance (ASA). , Cross-site scripting in Cisco Secure Firewall Adaptive Security Appliance (ASA).
How to Fix CVE-2026-20107: Insufficient granularity of access control in Cisco Application Policy. , Insufficient granularity of access control in Cisco Application Policy.
How to Fix CVE-2026-20089: Cisco Enterprise NFV Infrastructure Software (Bundle Sibling) , Cisco Enterprise NFV Infrastructure Software (Bundle Sibling)

Is CVE-2026-20033 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-2026-20033?

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-2026-20033?

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

Where is the official advisory for CVE-2026-20033?

The vendor advisory is at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-cpdos-qLsv6pFD. The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-20033.

References

Official vendor advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-cpdos-qLsv6pFD
NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20033
CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

*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.*