CVE-2023-41890 in Sustainsys.Saml2
Summary
by MITRE • 09/19/2023
Sustainsys.Saml2 library adds SAML2P support to ASP.NET web sites, allowing the web site to act as a SAML2 Service Provider. Prior to versions 1.0.3 and 2.9.2, when a response is processed, the issuer of the Identity Provider is not sufficiently validated. This could allow a malicious identity provider to craft a Saml2 response that is processed as if issued by another identity provider. It is also possible for a malicious end user to cause stored state intended for one identity provider to be used when processing the response from another provider. An application is impacted if they rely on any of these features in their authentication/authorization logic: the issuer of the generated identity and claims; or items in the stored request state (AuthenticationProperties). This issue is patched in versions 2.9.2 and 1.0.3. The `AcsCommandResultCreated` notification can be used to add the validation required if an upgrade to patched packages is not possible.
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Analysis
by VulDB Data Team • 09/19/2023
The Sustainsys.Saml2 library vulnerability CVE-2023-41890 represents a critical identity provider validation flaw that undermines the security of SAML2 authentication implementations in ASP.NET web applications. This vulnerability affects versions prior to 1.0.3 and 2.9.2, where the library fails to adequately validate the issuer of the Identity Provider during SAML2 response processing. The flaw stems from insufficient cryptographic validation mechanisms that allow malicious actors to manipulate SAML2 responses, effectively enabling identity spoofing attacks. The vulnerability specifically targets the core authentication flow where the library processes SAML2 responses and validates the issuing identity provider, creating a pathway for attackers to forge authentication responses that appear legitimate to the relying party.
The technical implementation of this vulnerability allows for two primary attack vectors that can compromise authentication systems. First, an attacker can craft a SAML2 response that appears to originate from a trusted identity provider, enabling unauthorized access to applications that rely on issuer validation for authentication decisions. Second, malicious end users can manipulate stored authentication state, causing the system to use session data intended for one identity provider when processing responses from another. This cross-provider state contamination can lead to privilege escalation, unauthorized data access, or complete authentication bypass scenarios. The vulnerability particularly impacts applications that depend on the issuer information within generated identities and claims, as well as those that utilize stored request state (AuthenticationProperties) for authorization logic enforcement. This weakness directly relates to CWE-287, which addresses authentication bypass through improper validation of credentials, and aligns with ATT&CK technique T1566.001 for credential harvesting through phishing attacks.
The operational impact of CVE-2023-41890 extends beyond simple authentication bypass to encompass potential data breaches and unauthorized system access. Applications relying on SAML2 authentication for enterprise access control, single sign-on implementations, and multi-factor authentication systems become vulnerable to sophisticated attacks where attackers can impersonate legitimate users or identity providers. The vulnerability is particularly dangerous in environments where authentication logic depends on issuer-specific claims or state management, as it allows attackers to manipulate session contexts and potentially gain elevated privileges. Organizations using the affected library versions face significant risk exposure, especially in scenarios where the authentication system's integrity is crucial for maintaining security boundaries and access controls. The impact is amplified when applications store sensitive information in AuthenticationProperties or make authorization decisions based on issuer validation, as these systems become vulnerable to manipulation through crafted SAML2 responses.
Mitigation strategies for CVE-2023-41890 primarily focus on immediate remediation through package upgrades to versions 1.0.3 or 2.9.2, which contain the necessary validation fixes. Organizations should prioritize updating their SAML2 implementation libraries as a critical security measure, particularly in environments with high-security requirements or sensitive data access controls. For scenarios where immediate upgrades are not feasible, the library provides the AcsCommandResultCreated notification mechanism as a workaround, allowing developers to implement custom validation logic before response processing. This approach requires careful implementation to ensure proper issuer validation and state management, aligning with security best practices for authentication system hardening. Organizations should also conduct comprehensive security assessments of their SAML2 implementations, reviewing all authentication logic that depends on issuer information or stored state to identify potential attack vectors. The vulnerability highlights the importance of proper cryptographic validation in identity federation systems and underscores the necessity of implementing robust security controls around authentication state management and identity provider verification processes.