On a recent penetration test, our team discovered a high-risk vulnerability in a Medical System’s Single Sign-On (SSO) implementation that allows for user impersonation.
The Medical System’s Nginx server supports authentication in 2 forms:
Username and password authentication via REST API
Windows NTLM authentication over HTTP
The system includes a user management module that allows for creation of new users, defining relevant permissions and setting authentication type (either Windows authentication or not).
The team realized that it is the responsibility of the NGNIX to perform the authentication, then the identity is passed to the application and the application is responsible for enforcing authorization. If the user identity is not defined in the users’ table - the login will fail.
The Danger of Insufficient User Validation
During the penetration test, the team discovered that the application only stores the username part and not the entire domain/user scheme. That led us to believe that we can use local users with the same name and impersonate domain users. A short test proved us to be correct and the team successfully authenticated to the system using a user we built on a local machine.
This behavior allows for user impersonation and effectively bypasses the implemented authentication mechanism.
A malicious actor could leverage this technique to escalate system privileges and gain access as the application’s administrator. The risk and impact of this vulnerability are both high, with a medium probability of occurrence.
Impact of User Impersonation Vulnerability
The impact of this vulnerability is significant because it allows for user impersonation and effectively bypasses the implemented authentication mechanism. This means that a malicious actor could gain unauthorized access to sensitive information and resources within the Medical System.
Furthermore, if a malicious actor were to leverage this technique to escalate system privileges and gain access as the application’s administrator, they could potentially cause significant harm to the Medical System and its patients.
Mitigating User Impersonation Vulnerability
To mitigate this risk, it is recommended not to build proprietary authentication and authorization mechanisms in your application. If you need to use a non-standard solution (e.g. use both windows authentication and username/password authentication) make sure you review the design with professionals that fully understand the underlying protocols (such as NTLM, Kerberos or any other).
It is crucial for organizations to take this vulnerability seriously and implement preventative measures such as regular security audits, penetration testing, and vulnerability scanning to prevent user impersonation in their SSO implementations. Failing to do so could result in severe consequences for both the organization and its patients.
What other measures is your organization taking to prevent user impersonation in SSO implementations? Is Your Medical System’s SSO at Risk? Don’t let your organization fall victim to user impersonation! Get in touch with our security experts to find out how to protect your Medical System and keep your patients’ data safe.
What is user impersonation in the context of Single Sign-On (SSO) implementation? User impersonation is a technique used by malicious actors to gain access to a system or application by assuming the identity of an authorized user. In the context of SSO, user impersonation occurs when a faulty implementation allows a user to authenticate as another user.
What are some common causes of inappropriate SSO implementation? Inappropriate SSO implementation can be caused by several factors, including lack of validation for user authentication, insufficient validation of whether or not the user is part of the authorized domain, and storing only the username instead of the entire domain/user scheme.
What are the potential risks of inappropriate SSO implementation? Inappropriate SSO implementation can lead to user impersonation and effectively bypass the implemented authentication mechanism. This can result in unauthorized access to sensitive information and resources within the application or system. Furthermore, if a malicious actor were to leverage this technique to escalate system privileges and gain access as the application’s administrator, they could potentially cause significant harm to the organization.
Can user impersonation be detected? Yes, user impersonation can be detected by monitoring user authentication attempts and identifying abnormal behavior, such as users logging in from unfamiliar locations or devices.
How can organizations prevent user impersonation in their SSO implementation? Organizations can prevent user impersonation by validating that the user is a member of a predefined AD group before looking for a username in the database. Additionally, storing the full domain user and validating it can help prevent user impersonation.
What are some best practices for securing SSO implementation against user impersonation vulnerabilities? Best practices for securing SSO implementation against user impersonation vulnerabilities include implementing multi factor authentication, regularly reviewing and updating user access controls, and conducting regular vulnerability assessments and penetration testing.
Can organizations be held liable for the consequences of a faulty SSO implementation? Yes. Failing to implement appropriate security measures can result in legal and financial consequences, as well as reputational damage. It is essential for organizations to take user impersonation vulnerabilities seriously and implement appropriate security measures to prevent them.
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