CVE-2026-69395 in Windows
Summary
by MITRE • 09/08/2026
Use of externally-controlled format string in Active Directory Certificate Services (AD CS) allows an authorized attacker to disclose information over a network.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability described involves the improper handling of user-supplied input within Microsoft's Active Directory Certificate Services, specifically manifesting as a use of externally controlled format strings. This class of flaw is formally categorized under Common Weakness Enumeration identifier CWE-134 and represents a critical security defect where an application uses untrusted data in a call to a function that processes formatting directives without proper validation or sanitization. In the context of Active Directory Certificate Services, this typically occurs when processing certificate requests or managing certificate templates where specific fields are passed through logging mechanisms, error reporting routines, or internal string manipulation functions that interpret special characters as format specifiers rather than literal data.
An authorized attacker who possesses valid credentials within the domain can exploit this weakness to disclose sensitive information over the network. The operational impact stems from the ability of an attacker to inject specific format specifier sequences into input fields such as subject names, alternative names, or other certificate attributes. When these inputs are processed by vulnerable functions in AD CS components like certsrv.dll, the service attempts to interpret them according to standard C-style formatting rules. This misinterpretation can lead to the reading of arbitrary memory locations on the server stack and heap, resulting in the disclosure of internal system data that was not intended for public view.
The exploitation vector is particularly concerning because it requires authentication, meaning only users with existing access rights within the Active Directory environment can trigger this condition. However, given that many enterprise environments rely heavily on AD CS for issuing digital certificates to employees and devices, an insider threat or a compromised account provides sufficient privilege to initiate the attack. The disclosed information may include stack addresses, pointers to other data structures, or potentially sensitive configuration details stored in memory adjacent to the formatted string buffer. This leakage can aid further exploitation by revealing memory layout information useful for bypassing security mitigations such as Address Space Layout Randomization.
From a threat intelligence perspective, this vulnerability aligns with techniques observed in advanced persistent threats where attackers leverage legitimate administrative tools and services to maintain access or gather reconnaissance data without triggering immediate alarms due to the use of valid credentials. It falls under the broader category of information disclosure vulnerabilities which are often precursors to more severe exploits such as remote code execution if combined with other memory corruption flaws, although this specific instance primarily facilitates unauthorized information retrieval.
Mitigation strategies should focus on both technical controls and procedural updates. Microsoft has released security patches that address these format string handling issues within Active Directory Certificate Services; therefore, applying the latest cumulative updates is the primary remediation step. Administrators must ensure that all domain controllers running AD CS roles are patched promptly to close this information leakage channel. Additionally, implementing strict input validation on certificate request fields can prevent malformed or maliciously crafted strings from reaching vulnerable processing functions. Network segmentation and monitoring for unusual patterns in certificate requests may also help detect attempted exploitation activities before they result in significant data exposure.