CVE-2026-87944 in SAML SSO Module
Summary
by MITRE • 10/22/2026
Improper Certificate Validation vulnerability in Drupal SAML SSO - Service Provider allows Adversary in the Middle (AiTM). 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 cryptographic validation within the Drupal SAML SSO Service Provider module, specifically affecting version ranges from 0.0.0 through 3.2.0. This flaw stems from improper certificate validation mechanisms that are essential for establishing trust during the Security Assertion Markup Language authentication process. In standard SAML implementations, the service provider must rigorously verify the digital signatures of assertions received from identity providers to ensure they originate from a trusted source and have not been altered in transit. The deficiency in this module allows an adversary positioned between the client and the identity provider to intercept, modify, or forge these authentication responses without detection. By bypassing certificate validation checks, the attacker can manipulate the SAML assertion payload, effectively impersonating legitimate users or injecting false authentication states into the Drupal application.
From a technical perspective, the root cause lies in the failure to strictly enforce X509 certificate chain verification and signature algorithm constraints during the parsing of incoming SAML responses. When an identity provider signs a SAML assertion, it uses its private key corresponding to a public certificate that must be trusted by the service provider. The vulnerability allows for scenarios where invalid certificates are accepted, self-signed certificates in production environments are not rejected as expected, or signature algorithms deemed weak are permitted without sufficient scrutiny. This lack of strict validation creates an opening for Man-in-the-Middle attacks, commonly referred to as Adversary in the Middle or AiTM. In such a scenario, the attacker intercepts the SAML response from the identity provider and alters critical attributes within the assertion, such as changing the user identifier or role assignments, before forwarding it to the Drupal application. Because the service provider fails to validate that the signature corresponds to a trusted certificate with valid parameters, it accepts the tampered data as authentic.
The operational impact of this vulnerability is severe, potentially leading to complete compromise of authentication integrity and unauthorized access to sensitive resources within the Drupal environment. An attacker leveraging this flaw can escalate privileges by modifying role assignments in the SAML assertion, thereby gaining administrative or elevated user rights without valid credentials. Furthermore, it facilitates account takeover attacks where an adversary can authenticate as any existing user by forging a signed assertion that maps their identity to a target victim's account. This undermines the fundamental security guarantee of single sign-on systems, which rely on the assumption that assertions from trusted identity providers are immutable and authentic. The ability to bypass these checks effectively nullifies the authentication layer, allowing malicious actors to access confidential data, modify content, or establish persistent backdoors within the application infrastructure.
This vulnerability aligns with CWE-295 Improper Certificate Validation and falls under MITRE ATT&CK technique T1606 Weaponization for SAML-based attacks. To mitigate this risk, organizations must immediately upgrade the Drupal SAML SSO Service Provider module to a version greater than 3.2.0 where these validation checks have been corrected. Administrators should also enforce strict configuration policies that require specific trusted certificates and disable any legacy or weak signature algorithms such as SHA-1 if they are still enabled by default. Implementing additional monitoring for anomalous SAML assertion patterns can provide early detection of exploitation attempts, while ensuring that all identity provider metadata is regularly audited to confirm the integrity of public keys used in the trust chain.