CVE-2018-7644 in SimpleSAMLphp
Summary
by MITRE
The XmlSecLibs library as used in the saml2 library in SimpleSAMLphp before 1.15.3 incorrectly verifies signatures on SAML assertions, allowing a remote attacker construct a crafted SAML assertion on behalf of an Identity Provider that would pass as cryptographically valid, thereby allowing them to impersonate a user from that Identity Provider, aka a key confusion issue.
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Analysis
by VulDB Data Team • 02/16/2023
The XmlSecLibs library vulnerability CVE-2018-7644 represents a critical cryptographic weakness in the SimpleSAMLphp authentication framework that fundamentally undermines the security of SAML-based single sign-on implementations. This flaw exists within the signature verification process of SAML assertions, specifically when the saml2 library processes cryptographic signatures from identity providers. The vulnerability enables attackers to exploit a key confusion issue where maliciously crafted SAML assertions can appear cryptographically valid even when they originate from unauthorized sources rather than legitimate identity providers. The root cause lies in the improper handling of public key verification within the XML security library, which fails to properly validate the cryptographic binding between the signature and the expected identity provider's key material. This weakness allows adversaries to construct forged SAML assertions that bypass authentication checks, effectively enabling impersonation attacks against users and systems relying on the vulnerable SimpleSAMLphp implementations.
The technical implementation of this vulnerability stems from a failure in the XML signature validation process where XmlSecLibs does not adequately verify that the signature algorithm and key parameters match the expected cryptographic context of the identity provider. This misconfiguration creates a scenario where an attacker can manipulate the SAML assertion structure to include their own signature while maintaining the appearance of legitimacy. The flaw operates at the cryptographic protocol level, specifically affecting the XML Digital Signature standard implementation within the library. According to CWE classification, this represents a weakness in cryptographic implementation (CWE-327) combined with improper certificate validation (CWE-295), creating a dangerous combination that allows attackers to bypass authentication mechanisms entirely. The vulnerability manifests when the library fails to properly enforce key usage constraints and signature algorithm validation, enabling what security researchers categorize as a key confusion attack pattern.
The operational impact of CVE-2018-7644 extends far beyond simple authentication bypass, as it fundamentally compromises the trust model that SAML-based authentication systems rely upon for secure user identification and authorization. Organizations using vulnerable SimpleSAMLphp versions face the risk of unauthorized access to sensitive systems, data breaches, and potential lateral movement within their networks through compromised user sessions. The attack vector requires only that an attacker can intercept or generate SAML assertions, making it particularly dangerous in environments where SAML traffic flows through public or untrusted networks. This vulnerability directly maps to ATT&CK technique T1566.002 (Phishing for Information) and T1078.004 (Valid Accounts: Cloud Accounts), as attackers can leverage the forged assertions to gain access to cloud-based services and applications that depend on SAML authentication. The implications are severe for identity and access management systems, as the vulnerability undermines the core principle of cryptographic authentication and allows for impersonation of legitimate users and identity providers.
Mitigation strategies for CVE-2018-7644 require immediate patching of SimpleSAMLphp installations to version 1.15.3 or later, which contains the necessary fixes to properly validate SAML assertion signatures. Organizations should also implement additional security controls such as monitoring for unusual authentication patterns and implementing strict certificate validation policies for identity providers. Network segmentation and traffic inspection can help detect anomalous SAML assertion traffic patterns that may indicate exploitation attempts. Security teams should conduct thorough vulnerability assessments of all SAML-based authentication systems and ensure proper key management practices are in place. The fix addresses the underlying cryptographic validation issues by implementing proper signature algorithm verification and ensuring that the XML signature validation process correctly validates the relationship between the signature and the expected public key material. Additionally, organizations should consider implementing security controls that enforce strict certificate pinning for identity providers and regularly audit their SAML assertion handling processes to prevent similar vulnerabilities from emerging in other components of their authentication infrastructure.