CVE-2025-6444 in ServiceStack
Summary
by MITRE • 06/25/2025
ServiceStack GetErrorResponse Improper Input Validation NTLM Relay Vulnerability. This vulnerability allows remote attackers to relay NTLM credentials on affected installations of ServiceStack. Interaction with this library is required to exploit this vulnerability but attack vectors may vary depending on the implementation.
The specific flaw exists within the implementation of the GetErrorResponse method. The issue results from the lack of proper validation of user-supplied data, which can result in a type confusion condition. An attacker can leverage this vulnerability to relay NTLM credentials in the context of the current user. Was ZDI-CAN-25834.
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Analysis
by VulDB Data Team • 08/09/2025
The CVE-2025-6444 vulnerability represents a critical security flaw in ServiceStack's GetErrorResponse method that enables NTLM credential relay attacks. This vulnerability falls under the CWE-20 category of Improper Input Validation, specifically manifesting as a type confusion condition that occurs when the system fails to properly validate user-supplied data. The flaw exists within the NTLM authentication handling mechanism of ServiceStack, creating a pathway for remote attackers to exploit the system's trust relationships. The vulnerability requires interaction with the ServiceStack library to be exploited, making it particularly dangerous in environments where this framework is widely deployed. Attackers can leverage this weakness to capture and relay NTLM authentication tokens, effectively impersonating users within the network infrastructure. The issue was identified and tracked as ZDI-CAN-25834, indicating its recognition within the cybersecurity community as a significant threat vector.
The technical implementation of this vulnerability stems from insufficient validation within the GetErrorResponse method which processes error responses in ServiceStack applications. When user-supplied data is improperly handled during error processing, it creates opportunities for type confusion attacks that can manipulate the authentication flow. The lack of proper input validation means that malicious actors can craft specific payloads that exploit the library's handling of NTLM credentials. This flaw operates at the protocol level where NTLM authentication tokens can be intercepted and relayed without proper authentication checks. The vulnerability's impact extends beyond simple credential theft as it enables attackers to escalate privileges and move laterally within network environments. The attack vector is particularly concerning because it can be exploited through various implementation paths depending on how ServiceStack is integrated into different applications and systems.
From an operational perspective, this vulnerability poses significant risks to organizations relying on ServiceStack for their web services and API implementations. The NTLM relay capability allows attackers to leverage existing authentication infrastructure to gain unauthorized access to resources, potentially leading to complete system compromise. The vulnerability's exploitation requires minimal privileges and can be automated, making it attractive to both skilled and less sophisticated attackers. Organizations with Active Directory environments face particular risk as the relay attack can be used to access domain controllers and other privileged systems. The attack can occur without direct user interaction, making detection more challenging and potentially allowing attackers to remain undetected for extended periods. This vulnerability directly aligns with ATT&CK technique T1550.003 for OS Credential Dumping and T1550.001 for Reversible Encryption, as it enables credential relay and authentication manipulation through improper input handling.
Mitigation strategies for CVE-2025-6444 should focus on immediate patching of affected ServiceStack installations to address the input validation flaws in the GetErrorResponse method. Organizations must implement network segmentation to limit the impact of potential credential relay attacks and monitor for unusual authentication patterns. The implementation of additional authentication layers such as multi-factor authentication can provide defense-in-depth against exploitation attempts. Security teams should also review and update their monitoring systems to detect anomalous NTLM authentication behavior that might indicate credential relay activity. Disabling NTLM authentication where possible and implementing Kerberos authentication instead can significantly reduce the attack surface. Regular security assessments of ServiceStack implementations are essential to identify and remediate similar vulnerabilities. The mitigation approach should also include network-level controls such as implementing authentication firewalls and monitoring for unauthorized authentication relay attempts. Organizations should consider implementing automated patch management processes to ensure rapid deployment of security updates and maintain comprehensive logging of authentication events for forensic analysis purposes.