● Medium · CVSS 6.5

How to Fix CVE-2026-23655: Critical Vulnerability in Microsoft ACI Confidential Containers

Q: Is CVE-2026-23655 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Q: Will a WAF or IDS rule fully mitigate CVE-2026-23655?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

Q: How long should I plan for the upgrade?

Typical vendor-documented upgrade windows for Microsoft ACI Confidential Containers run from a few minutes to under an hour depending on cluster size. Test in a staging environment first and follow the vendor's documented HA upgrade order.

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

How to Fix CVE-2026-27927: Race condition in Microsoft Windows — Race condition in Microsoft Windows
How to Fix CVE-2026-41094: Code Injection RCE in Microsoft Data Formulator — Code Injection RCE in Microsoft Data Formulator
How to Fix CVE-2026-26176: Heap buffer overflow in Microsoft Windows , Heap buffer overflow in Microsoft Windows
How to Fix CVE-2026-33825: Security Vulnerability in Microsoft Defender Antimalware Platform , Security Vulnerability in Microsoft Defender Antimalware Platform
How to Fix CVE-2026-20854: Use-After-Free in Windows 11 Version 24H2 , Use-After-Free in Windows 11 Version 24H2

*By Sai Kiran Pandrala*

⚡ At a glance


Severity	CVSS 6.5 - Medium
Actively exploited?	Not currently listed in CISA KEV
Affected	1.0.0 < 2.12
Fixed in	See vendor advisory
Type (CWE)	CWE-312: Cleartext Storage of Sensitive Information

What is CVE-2026-23655?

CVE-2026-23655 is a security flaw in Microsoft ACI Confidential Containers. Cleartext storage of sensitive information in Azure Compute Gallery allows an authorized attacker to disclose information over a network.

Why this CVE matters

Unpatched network-facing software is the leading initial-access vector in public breach reporting. Treat any CVSS-9 class flaw on an internet-reachable system as urgent, regardless of whether public exploit code has been observed yet.

For deployments of Microsoft ACI Confidential Containers that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Microsoft ACI Confidential Containers: 1.0.0 < 2.12

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

On Windows, check the product's installed version via Settings - Apps - Installed apps, or run Get-Package from PowerShell to enumerate installed versions.

How to fix CVE-2026-23655

Read the vendor advisory in full: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23655
Upgrade Microsoft ACI Confidential Containers to the patched build listed in the vendor advisory.
Back up the configuration (and database, where applicable) before upgrading.
Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
Restart the affected service so the patched binary loads, then verify the new version (see verification section).

Apply the Microsoft security update


# Target patched build: see advisory (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23655)
# Source advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23655

# Stage PSWindowsUpdate.
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck -Confirm:$false
Import-Module PSWindowsUpdate

# Install the cumulative / security rollup that ships the CVE-2026-23655 fix.
# Substitute the KB number listed in the advisory above.
Get-WindowsUpdate -AcceptAll -Install -AutoReboot

# Confirm the patch landed.
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5


# CVE-2026-23655 remediation runner.
$log = "C:\Logs\CVE-2026-23655-fix.log"
New-Item -ItemType Directory -Force -Path (Split-Path $log) | Out-Null
function Write-Log($msg) { "$(Get-Date -Format s) $msg" | Out-File $log -Append }

try {
    Write-Log "Detect: searching for Microsoft ACI Confidential Containers"
    $installed = Get-CimInstance Win32_Product -ErrorAction SilentlyContinue |
        Where-Object { $_.Name -match 'Microsoft ACI Confidential Containers' }
    if ($installed) { Write-Log "Found version $($installed.Version)" }

    Write-Log "Upgrade: applying Windows Update rollup"
    Install-WindowsUpdate -AcceptAll -AutoReboot -ErrorAction SilentlyContinue

    Write-Log "Verify"
    $after = Get-CimInstance Win32_Product | Where-Object { $_.Name -match 'Microsoft ACI Confidential Containers' }
    if ($after) { Write-Log "Post-patch version: $($after.Version)" }
} catch { Write-Log "ERROR: $_"; throw }


# Fleet inventory across Windows hosts via Ansible (WinRM).
ansible windows -m win_updates -a "category_names=SecurityUpdates state=installed"

Verify the fix landed


# 1. Confirm the running version matches the fixed-in version listed above.
# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag this CVE on the patched target.
# 3. Inspect recent service / kernel logs for crash-loops or rollback events.
journalctl --since "10 minutes ago" | tail -50
dmesg --since "10 minutes ago" 2>/dev/null | tail -50

If you cannot patch immediately

No official workaround exists beyond restricting network exposure to the affected component. Apply the vendor patch as the primary remediation.

How to verify the fix worked

After applying the patch, verify the running version in the product's admin UI or via the vendor-documented CLI command.
Confirm the patched build matches the version listed in the vendor advisory.
Run an authenticated vulnerability scan with a current signature set and confirm the scanner no longer flags CVE-2026-23655.
Review logs for the entire pre-patch window for indicators of compromise listed in the vendor or CISA advisory.
Confirm any network-layer mitigations that were applied as a stopgap have been reverted (or left in place intentionally) once the patch is verified.

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for log entries that do not match your normal request patterns, especially repeated requests to the same uncommon endpoint, and any administrative changes you cannot tie back to a known operator.

Frequently asked questions

Is CVE-2026-23655 being exploited in the wild?