CVE-2023-45683 in saml
Summary
by MITRE • 10/25/2023
github.com/crewjam/saml is a saml library for the go language. In affected versions the package does not validate the ACS Location URI according to the SAML binding being parsed. If abused, this flaw allows attackers to register malicious Service Providers at the IdP and inject Javascript in the ACS endpoint definition, achieving Cross-Site-Scripting (XSS) in the IdP context during the redirection at the end of a SAML SSO Flow. Consequently, an attacker may perform any authenticated action as the victim once the victim’s browser loaded the SAML IdP initiated SSO link for the malicious service provider. Note: SP registration is commonly an unrestricted operation in IdPs, hence not requiring particular permissions or publicly accessible to ease the IdP interoperability. This issue is fixed in version 0.4.14. Users unable to upgrade may perform external validation of URLs provided in SAML metadata, or restrict the ability for end-users to upload arbitrary metadata.
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Analysis
by VulDB Data Team • 11/03/2023
The vulnerability identified as CVE-2023-45683 affects the github.com/crewjam/saml Go library, a widely used implementation for SAML single sign-on operations. This flaw resides in the library's handling of Assertion Consumer Service (ACS) location URIs during SAML binding parsing processes. The issue stems from inadequate validation of the ACS endpoint definition, creating a path for malicious actors to manipulate the SAML flow without proper authorization. The vulnerability specifically impacts the security of SAML identity providers that utilize this library for handling SAML assertions and redirects. The flaw allows attackers to register malicious service providers at the identity provider without requiring elevated permissions, as service provider registration is typically an open process designed to facilitate interoperability.
The technical implementation of this vulnerability occurs during the SAML SSO flow when the identity provider processes the ACS endpoint definition. The library fails to validate the ACS Location URI against the SAML binding requirements, enabling attackers to inject malicious JavaScript code into the ACS endpoint. This injection occurs during the redirection phase of the SAML flow, when the victim's browser is directed to the malicious service provider's endpoint. The vulnerability directly maps to CWE-79 Cross-Site Scripting, as the malicious script executes in the context of the identity provider's domain. The attack leverages the trust relationship between the identity provider and service provider, using the legitimate SAML SSO flow to deliver malicious payloads.
The operational impact of this vulnerability extends beyond simple XSS exploitation, as it enables attackers to perform authenticated actions on behalf of victims within the identity provider's context. When victims click on SAML IdP-initiated SSO links for malicious service providers, the injected JavaScript executes in the victim's browser session, potentially allowing attackers to access sensitive information, modify user data, or perform administrative actions. This represents a significant threat to identity provider security, as the attack can be executed without requiring direct access to the identity provider's systems or user credentials. The vulnerability is particularly dangerous because service provider registration is typically unrestricted, making it easy for attackers to establish malicious endpoints without detection. The attack follows ATT&CK technique T1566.002 for credential harvesting through SAML-based attacks.
Mitigation strategies for this vulnerability include upgrading to version 0.4.14 of the library, which contains the necessary validation fixes. Organizations unable to upgrade immediately should implement external validation of URLs provided in SAML metadata to ensure they conform to expected patterns and domains. Additionally, administrators can restrict the ability for end-users to upload arbitrary SAML metadata, requiring manual approval or automated validation of metadata before acceptance. Network-level controls can also be implemented to monitor for suspicious URL patterns in SAML flows, and organizations should consider implementing Content Security Policy headers to limit script execution in SAML contexts. The vulnerability highlights the importance of proper input validation in security-critical libraries and demonstrates how seemingly minor validation gaps can lead to significant security implications in identity management systems.