CVE-2026-62818: AD CS Use After Free Vulnerability

CVE-2026-62818 Overview

CVE-2026-62818 is a use-after-free vulnerability in Microsoft Active Directory Certificate Services (AD CS). An authorized attacker can trigger the flaw over a network to execute arbitrary code on the affected server. The vulnerability is tracked under CWE-416: Use After Free and requires low privileges with no user interaction. Successful exploitation leads to full compromise of confidentiality, integrity, and availability on the certificate services host.

Critical Impact
An authenticated attacker with low privileges can achieve remote code execution on AD CS servers, enabling compromise of certificate issuance infrastructure that underpins enterprise authentication and trust.

Affected Products

Microsoft Active Directory Certificate Services (AD CS)
Windows Server deployments running the AD CS role
Refer to the Microsoft CVE-2026-62818 Advisory for the authoritative list of affected builds

Discovery Timeline

2026-08-11 - CVE-2026-62818 published to NVD
2026-08-12 - Last updated in NVD database

Technical Details for CVE-2026-62818

Vulnerability Analysis

CVE-2026-62818 is a use-after-free flaw in the AD CS service. The service handles certificate enrollment, issuance, and revocation requests from domain-joined clients. A memory object referenced during request processing is freed while a dangling pointer remains reachable. Subsequent operations on that pointer allow an attacker to influence the freed memory region and hijack control flow. Because AD CS runs with elevated service privileges, successful exploitation grants code execution in a context that can sign, issue, or revoke certificates across the enterprise.

Root Cause

The root cause is improper object lifetime management within AD CS request handling. A code path releases an allocation without clearing all references, then reuses the pointer during a subsequent operation. This matches the CWE-416 pattern where freed memory is reallocated with attacker-influenced content before the stale reference is dereferenced.

Attack Vector

The attack vector is network-based and requires an authenticated session with low privileges. The attacker sends crafted certificate service requests over standard AD CS protocols to reach the vulnerable code path. No user interaction is required. Detailed exploitation mechanics are not public. Consult the Microsoft CVE-2026-62818 Advisory for vendor guidance. No public proof-of-concept code was available at the time of publication, and CVE-2026-62818 is not listed in the CISA Known Exploited Vulnerabilities catalog.

// No verified exploitation code is publicly available for CVE-2026-62818.
// Refer to the Microsoft advisory for technical details.

Detection Methods for CVE-2026-62818

Indicators of Compromise

Unexpected AD CS service crashes, restarts, or Windows Error Reporting entries referencing certsrv.exe
Anomalous certificate enrollment requests from low-privileged accounts or unusual source hosts
New or unexpected certificates issued by the enterprise Certificate Authority, particularly for privileged identities
Outbound network connections initiated by the AD CS service process to non-standard destinations

Detection Strategies

Monitor Windows Event Logs on CA servers for CertificationAuthority errors and abnormal RPC/DCOM activity
Correlate authentication events with certificate issuance events to identify low-privileged principals triggering enrollment paths
Alert on child processes spawned by certsrv.exe, which should not launch shells or scripting hosts

Monitoring Recommendations

Enable AD CS auditing and forward Security, System, and Application logs to a centralized SIEM
Baseline normal enrollment volume per account and flag deviations
Track service process memory anomalies and unexpected module loads within the AD CS process

How to Mitigate CVE-2026-62818

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-62818 Advisory to all servers running the AD CS role
Inventory certificate authorities and confirm patch status on each CA, including subordinate and offline-capable CAs
Review recently issued certificates for signs of abuse and revoke any that cannot be validated
Restrict which accounts can submit certificate requests to the CA to the minimum required set

Patch Information

Microsoft has issued a security update addressing CVE-2026-62818. The authoritative patch details, affected build numbers, and download links are available in the Microsoft CVE-2026-62818 Advisory. Apply the update through Windows Update, WSUS, or your standard patch management workflow after validating in a test environment.

Workarounds

Limit network reachability of AD CS enrollment endpoints to trusted management networks using host and network firewalls
Tighten certificate template permissions so only required security principals can enroll or request certificates
Disable unused AD CS enrollment interfaces such as web enrollment where they are not required

bash

# Example: restrict inbound RPC to the CA to a management subnet on Windows
New-NetFirewallRule -DisplayName "Restrict AD CS RPC" `
  -Direction Inbound `
  -Protocol TCP `
  -LocalPort 135 `
  -RemoteAddress 10.10.20.0/24 `
  -Action Allow