The Security Assertion Markup Language (SAML) is a widely used standard in single sign-on systems. In a simplified version, the user authenticates to an Identity Provider which generates a signed SAML Response. This response is then forwarded to a Service Provider for validation and authentication.
If the Service Provider does not manage to properly validate the incoming SAML response message signatures, attackers might be able to manipulate the response content without the application noticing. Especially, they might be able to alter the authentication-targeted user.
By exploiting this vulnerability, an attacker can manipulate the SAML Response to impersonate a different user. This, in turn, can have various consequences on the application's security.
Exploiting this vulnerability allows an attacker with authenticated access to impersonate other users within the SAML-based SSO system. This can lead to unauthorized access to sensitive information, resources, or functionalities the attacker should not have. By masquerading as legitimate users, the attacker can bypass authentication mechanisms and gain unauthorized privileges, potentially compromising the entire system. By impersonating a user with higher privileges, the attacker can gain access to additional resources. Privilege escalation can lead to further compromise of other systems and unauthorized access to critical infrastructure.
With the ability to impersonate other users, an attacker can gain access to sensitive data stored within the SAML-based SSO system. This includes personally identifiable information (PII), financial data, intellectual property, or any other confidential information. Data breaches can result in reputational damage, legal consequences, financial losses, and harm to individuals whose data is exposed.
The following code examples are vulnerable because they explicitly include comments in signature checks. An attacker is able to change the field identifying the authenticated user with XML comments.
* Spring blog - https://spring.io/blog/2018/03/01/spring-security-saml-and-this-week-s-saml-vulnerability[Spring Security SAML and this week's SAML Vulnerability]
* Spring Security SAML - https://github.com/spring-projects/spring-security-saml/issues/228[Issue #228 Multiple SAML libraries may allow authentication bypass via incorrect XML canonicalization and DOM traversal]
* OWASP - https://owasp.org/www-project-top-ten/2017/A9_2017-Using_Components_with_Known_Vulnerabilities[Top 10 2017 Category A9 - Using Components with Known Vulnerabilities]
