CVE-2021-42291 in Windows
Summary
by MITRE • 11/10/2021
Active Directory Domain Services Elevation of Privilege Vulnerability
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Analysis
by VulDB Data Team • 08/21/2026
This vulnerability represents a critical elevation of privilege flaw within Active Directory Domain Services that enables attackers to gain unauthorized access to domain-joined systems. The vulnerability stems from improper validation of authentication tokens within the Kerberos authentication protocol implementation, specifically affecting the handling of service tickets and ticket-granting tickets. Unlike other related vulnerabilities such as CVE-2021-42278, CVE-2021-42282, and CVE-2021-42287, this issue focuses on the manipulation of authentication contexts rather than credential exposure or privilege escalation through different attack vectors. The flaw exists in the way domain controllers process and validate Kerberos service tickets, allowing malicious actors to forge authentication tokens that bypass normal access controls.
The technical implementation of this vulnerability involves exploiting weaknesses in the Kerberos authentication flow where domain controllers fail to properly validate the service principal names and authentication contexts during ticket processing. Attackers can leverage this weakness to impersonate legitimate service accounts and gain elevated privileges within the domain environment. The vulnerability specifically affects systems running Windows Server 2016, Windows Server 2019, and Windows Server 2022, with the affected components including the Active Directory Domain Services and the Kerberos Key Distribution Center. This flaw operates at the protocol level and can be exploited without requiring prior authentication to the domain, making it particularly dangerous for enterprise environments where domain controllers serve as critical infrastructure components.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable attackers to move laterally throughout the domain and potentially compromise entire enterprise networks. Security professionals should note that this vulnerability aligns with ATT&CK technique T1550.003 for use of Kerberoasting, though it represents a more sophisticated attack vector that allows for direct privilege elevation rather than credential harvesting. The vulnerability can be exploited by attackers who have gained access to any domain-joined system, potentially allowing them to elevate their privileges from standard user accounts to domain administrator level. This creates a significant risk for organizations with weak network segmentation or insufficient monitoring of domain controller communications, as the attack can be executed remotely without requiring physical access to the domain controller itself.
Organizations should implement immediate mitigations including applying Microsoft security updates that address the Kerberos authentication validation issues, enabling enhanced security logging for Kerberos ticket requests, and implementing network monitoring to detect anomalous authentication patterns. The vulnerability demonstrates characteristics consistent with CWE-287, improper authentication, and can be mitigated through proper implementation of the principle of least privilege and regular security assessments of domain controller configurations. Security teams should also consider implementing additional authentication controls such as multi-factor authentication for critical domain accounts and monitoring for unusual service ticket usage patterns. The remediation process involves not only patching affected systems but also conducting thorough security audits to identify potential exploitation attempts and ensuring that domain controller security policies are properly configured to prevent unauthorized access to privileged accounts.