CVE-2026-73025 in Windows
Summary
by MITRE • 09/08/2026
Weak authentication in Windows iSCSI allows an unauthorized attacker to bypass a security feature over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified within the Microsoft Internet Small Computer Systems Interface (iSCSI) initiator component represents a critical failure in the implementation of authentication protocols, specifically allowing for the circumvention of established security controls during session establishment. This flaw stems from an insufficient validation mechanism when processing incoming connection requests or challenge-response sequences, which are fundamental to ensuring that only authorized entities can access storage resources over the network. The iSCSI protocol relies heavily on mutual authentication mechanisms such as CHAP (Challenge-Handshake Authentication Protocol) or MSCHAPv2 to verify the identity of both the initiator and the target. When these protocols are misconfigured, improperly implemented, or exploited due to a logic error in the handling of credentials, an attacker can bypass the requirement for valid user names or passwords entirely. This weakness is not merely a configuration issue but often reflects a deeper architectural flaw where the software fails to enforce strict adherence to authentication standards before granting access to block devices and storage volumes.
From a technical perspective, this vulnerability allows an unauthorized actor operating on the same network segment to intercept traffic or send crafted packets that exploit the gap in verification logic. By manipulating the handshake process or exploiting race conditions during the authentication phase, the attacker can trick the iSCSI service into accepting the connection as legitimate without providing valid credentials. This effectively neutralizes one of the primary layers of defense for storage area networks (SANs), which often assume that network-level access controls are sufficient when combined with protocol-level security. The ability to bypass these checks means that sensitive data stored on remote targets becomes accessible to any entity capable of reaching the iSCSI port, typically TCP port 3260 or its secure variant over TLS. This scenario is particularly dangerous in enterprise environments where storage resources are shared across multiple hosts and applications, as it can lead to unauthorized read/write access to critical databases, virtual machine images, and system files.
The operational impact of this vulnerability extends beyond simple data exfiltration. An attacker with the ability to bypass authentication gains full control over the iSCSI session, which translates directly into privilege escalation at the storage layer. This allows for the deletion, modification, or encryption of stored data, leading to severe availability and integrity compromises. In a worst-case scenario, this can facilitate ransomware attacks by allowing malware writers to encrypt shared storage volumes before they are backed up or isolated. Furthermore, because iSCSI is often used in high-availability clusters, compromising one node through this vulnerability could potentially allow lateral movement across the cluster if session tokens or credentials are reused or cached improperly. The lack of proper authentication also undermines compliance with regulatory frameworks that mandate strict access controls for data at rest and in transit, such as PCI DSS, HIPAA, and GDPR, exposing organizations to significant legal and financial repercussions.
This flaw aligns closely with CWE-287, which describes Improper Authentication, specifically the failure to verify credentials or bypass authentication mechanisms. It also maps to MITRE ATT&CK technique T1078, Valid Accounts, as it enables an attacker to use legitimate-looking sessions without possessing valid credentials, effectively impersonating a trusted system component. Additionally, depending on the specific exploitation vector, it may relate to CWE-352, Cross-Site Request Forgery (CSRF), if web-based management interfaces for iSCSI targets are involved and fail to validate session integrity during authentication requests. The vulnerability underscores the importance of defense-in-depth strategies where network segmentation is complemented by robust protocol-level security implementations that strictly enforce cryptographic challenges and responses without exception or fallback to insecure defaults.
Mitigation requires a multi-faceted approach focusing on both configuration hardening and architectural improvements. Organizations should immediately ensure that iSCSI services are not exposed to untrusted networks, utilizing firewalls to restrict access to known initiator IP addresses only. Enabling mutual authentication with strong cryptographic algorithms such as SHA-256 or stronger for CHAP is essential, along with the use of TLS encryption to protect data in transit from eavesdropping and man-in-the-middle attacks that could otherwise exploit weak session handling. Regular auditing of iSCSI configurations should be conducted to disable any legacy authentication methods like plain-text passwords if they are still enabled by default or due to compatibility issues. Furthermore, applying the latest security patches provided by Microsoft is critical, as these updates often contain fixes for logic errors in protocol handlers that allow such bypasses. Implementing network access control (NAC) solutions can also help ensure that only authorized devices with valid certificates or credentials are permitted to establish connections to iSCSI targets, thereby reducing the attack surface significantly and maintaining the integrity of storage infrastructure against unauthorized access attempts.