CVE-2026-87947 in SAML SSO Module
Summary
by MITRE • 10/22/2026
Improper Verification of Cryptographic Signature vulnerability in Drupal SAML SSO - Service Provider allows Signature Spoof. This issue affects SAML SSO - Service Provider versions: from 0.0.0 to 3.2.0.
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Analysis
by VulDB Data Team • 10/22/2026
The identified vulnerability represents a critical failure in the cryptographic verification process within the Drupal module for Single Sign-On (SSO) using Security Assertion Markup Language, specifically affecting the Service Provider component across versions ranging from initial releases up through version 3.2.0. This flaw stems directly from an improper validation of digital signatures attached to SAML assertions or responses received by the application. In a properly secured implementation, every incoming assertion must be cryptographically verified against the trusted public key associated with the Identity Provider to ensure both integrity and authenticity. The absence of this rigorous check allows attackers to bypass authentication mechanisms entirely, as the system accepts forged credentials that have not been validated for origin or content modification.
From a technical perspective, SAML relies heavily on XML Digital Signatures to guarantee that assertions issued by an Identity Provider are genuine and have not been altered in transit. When the Service Provider fails to verify these signatures, it effectively treats any well-formed SAML response as legitimate regardless of its source. This creates a scenario where an attacker can craft arbitrary SAML responses containing claims for administrative users or other privileged accounts. By manipulating elements such as NameID attributes and role assignments within the assertion payload, the adversary can impersonate high-privilege entities without possessing valid credentials from the Identity Provider. The vulnerability exploits the trust relationship between systems by breaking the chain of cryptographic verification that is fundamental to federated identity architectures.
The operational impact of this weakness is severe, potentially leading to complete compromise of the Drupal application and any downstream services relying on it for authentication. An attacker can achieve unauthorized access with administrative privileges, allowing them to modify site configurations, inject malicious code, exfiltrate sensitive data, or establish persistent backdoors within the system. Since SAML is often used in enterprise environments where users log into multiple applications via a central identity source, this vulnerability could facilitate broader lateral movement if the compromised Drupal instance holds keys or access tokens for other integrated services. The ability to spoof signatures means that traditional audit logs may record successful authentications from legitimate sources even though they were actually forged by an attacker, complicating forensic analysis and incident response efforts significantly.
This flaw aligns with Common Weakness Enumeration identifier CWE-347, which describes Improper Verification of Cryptographic Signature, indicating a failure to ensure the integrity or authenticity of data protected by cryptographic means. Furthermore, in the context of the MITRE ATT&CK framework, this vulnerability facilitates techniques related to Account Manipulation and Credential Access, specifically allowing attackers to create unauthorized accounts or modify existing ones through forged identity assertions. It also relates to Defense Evasion as it allows bypassing authentication controls that are designed to restrict access to sensitive resources. The lack of signature verification undermines the core security principles of non-repudiation and integrity assurance inherent in SAML-based federations.
Mitigation strategies must prioritize immediate remediation by upgrading the Drupal module to a version later than 3.2.0 where this validation logic has been corrected. Until an upgrade is feasible, administrators should implement strict input filtering at the web server or application firewall level to reject malformed SAML responses that lack expected signature structures. Additionally, enabling detailed logging for authentication failures and successes can help detect anomalous patterns indicative of exploitation attempts. It is also advisable to review existing user accounts for unauthorized privilege escalations resulting from potential past exploits. Long-term architectural improvements should include enforcing strict certificate pinning and regularly rotating signing keys used by Identity Providers to minimize the window of opportunity if a key compromise occurs, although this does not replace the need for proper signature verification on the Service Provider side.