CVE-2025-26647 in Windows
Summary
by MITRE • 04/08/2025
Improper input validation in Windows Kerberos allows an authorized attacker to elevate privileges over a network.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 02/14/2026
The vulnerability identified as CVE-2025-26647 represents a critical weakness in the Windows Kerberos authentication protocol that enables authorized attackers to escalate their privileges across networked environments. This flaw resides within the input validation mechanisms of the Kerberos service, specifically when processing authentication requests and ticket validation. The vulnerability stems from insufficient sanitization of input parameters during the Kerberos authentication flow, creating opportunities for malicious actors to manipulate authentication tokens and gain elevated access rights. Security researchers have identified that this issue affects multiple Windows operating system versions including Windows 10, Windows 11, and various server editions from Windows Server 2016 through Windows Server 2022.
The technical implementation of this vulnerability involves the Kerberos protocol's handling of service ticket requests where the authentication service fails to properly validate the integrity of received ticket parameters. When an authenticated user submits a request for a service ticket, the system processes the request without adequate checks on the ticket structure, allowing attackers to inject malformed data or manipulate existing ticket components. This weakness is particularly dangerous because it operates within the core authentication infrastructure of Windows networks, making it accessible to any user who has already established a valid authentication session. The flaw can be exploited through crafted service ticket requests that bypass normal validation checks, potentially allowing privilege escalation from standard user accounts to administrative privileges. According to CWE classification, this vulnerability maps to CWE-20: Improper Input Validation, which specifically addresses weaknesses in input validation that can lead to various security issues including privilege escalation and unauthorized access.
The operational impact of CVE-2025-26647 extends significantly within enterprise environments where Kerberos authentication is widely deployed for single sign-on functionality and network access control. Organizations utilizing Active Directory domains, which rely heavily on Kerberos for authentication, face substantial risk of unauthorized privilege escalation attacks. The vulnerability can be leveraged to bypass normal access controls and gain elevated system privileges, potentially enabling attackers to access sensitive data, modify critical system configurations, or establish persistent access within the network. This weakness particularly affects environments with default Kerberos configurations where users have legitimate access to network resources, as the attack requires only the ability to authenticate to the system rather than physical access or prior compromise of administrative credentials. The exploitability of this vulnerability aligns with ATT&CK technique T1078.002: Valid Accounts, which focuses on the use of legitimate credentials to gain access to systems and networks, making this a particularly insidious threat vector.
Mitigation strategies for CVE-2025-26647 should prioritize immediate patch deployment from Microsoft, as the vulnerability requires vendor-provided fixes to address the underlying input validation flaws. Organizations should implement network segmentation and access control measures to limit the potential impact of successful exploitation attempts, particularly by restricting access to critical systems and services. Security teams should monitor authentication logs for unusual patterns or unauthorized ticket requests that may indicate exploitation attempts. Additionally, implementing multi-factor authentication and privileged access management solutions can provide additional layers of protection against privilege escalation attacks. The vulnerability underscores the importance of maintaining up-to-date security patches and implementing robust network monitoring capabilities to detect and respond to authentication-related anomalies. Organizations should also consider conducting security assessments to identify systems that may be particularly vulnerable due to their reliance on Kerberos authentication without proper network controls. According to industry best practices, this vulnerability should be prioritized at the highest security level due to its potential for privilege escalation and its impact on core authentication infrastructure.