CVE-2026-69624: AD CS Input Validation Vulnerability

CVE-2026-69624 Overview

CVE-2026-69624 is a tampering vulnerability in Microsoft Active Directory Certificate Services (AD CS). The flaw stems from an incomplete list of disallowed inputs [CWE-184], which allows an authenticated attacker to submit crafted values that bypass server-side validation. A successful attack enables tampering with certificate-related data over the network. The vulnerability requires low privileges and no user interaction, and it affects integrity but not confidentiality or availability.

Critical Impact
An authorized attacker on the network can tamper with certificate issuance or related AD CS operations, undermining trust in the Public Key Infrastructure (PKI) that Active Directory depends on.

Affected Products

Microsoft Active Directory Certificate Services (AD CS)
Windows Server deployments running the AD CS role
Enterprise PKI environments issuing certificates through AD CS

Discovery Timeline

2026-09-08 - CVE-2026-69624 published to the National Vulnerability Database (NVD)
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-69624

Vulnerability Analysis

The vulnerability is classified under [CWE-184] Incomplete List of Disallowed Inputs. AD CS validates certificate request inputs against a denylist of prohibited values. Because that list is incomplete, specific inputs pass validation and reach downstream processing where they should have been rejected.

An authenticated attacker with low privileges can send crafted requests over the network to the AD CS service. The result is unauthorized modification of certificate-related data, which affects the integrity of the PKI without directly leaking data or halting service. AD CS is a foundational identity service, so tampering can cascade into authentication and authorization decisions across the domain.

Root Cause

The root cause is denylist-based input filtering that fails to enumerate every dangerous value. Denylist approaches are inherently fragile because attackers only need to find one input the filter missed. AD CS processes the unfiltered input in a context where it can alter certificate attributes or workflow behavior.

Attack Vector

Exploitation requires network access to AD CS and valid credentials in the target domain. The attacker submits crafted certificate service requests containing inputs that evade the disallow filter. No user interaction is needed, and the attack complexity is low. Technical details are limited in the public advisory. See the Microsoft Security Vulnerability CVE-2026-69624 advisory for authoritative information.

Detection Methods for CVE-2026-69624

Indicators of Compromise

Unexpected certificate issuance events in the AD CS logs, particularly for templates the requesting account should not use.
Certificate requests containing unusual Subject, Subject Alternative Name (SAN), or extension values from low-privilege accounts.
Modifications to certificate template configuration or issued certificate attributes without a corresponding change-management record.

Detection Strategies

Monitor Windows Event IDs 4886, 4887, 4888, and 4899 on Certificate Authority (CA) servers for anomalous certificate request and issuance activity.
Baseline expected certificate request patterns per account and alert on deviations such as new template use or altered SAN fields.
Correlate AD CS request telemetry with Active Directory authentication events to identify low-privilege accounts probing the CA.

Monitoring Recommendations

Forward CA operational and security logs to a centralized SIEM for long-term retention and correlation.
Enable CA auditing for all issued, revoked, and denied certificate requests through certutil -setreg CA\AuditFilter 127.
Review certificate template ACLs regularly and alert on template modifications or ACL changes.

How to Mitigate CVE-2026-69624

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-69624 to all servers running the AD CS role.
Inventory every CA in the environment, including subordinate and offline CAs, and prioritize enterprise-issuing CAs.
Audit accounts with enroll and autoenroll permissions on sensitive templates and remove unnecessary access.

Patch Information

Microsoft has published the security update through the Microsoft Security Response Center. Refer to the MSRC advisory for the specific KB article and affected Windows Server builds. Deploy the patch on all CA servers and reboot as required.

Workarounds

Restrict network access to CA servers so only trusted enrollment endpoints and authorized administrators can reach the AD CS interfaces.
Tighten certificate template permissions and disable templates that permit user-supplied Subject or SAN values where possible.
Enforce CA Manager approval on high-value templates until the patch is deployed.

bash

# Configuration example: enable comprehensive CA auditing and require manager approval
certutil -setreg CA\AuditFilter 127
net stop certsvc && net start certsvc
certutil -setreg policy\EditFlags +EDITF_ENABLEREQUESTEXTENSIONLIST