CVE-2026-87945 in SAML SSO Module
Summary
by MITRE • 10/22/2026
URL Redirection to Untrusted Site ('Open Redirect') vulnerability in Drupal SAML SSO - Service Provider allows Fake the Source of Data. 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 security flaw within the Drupal module for SAML Single Sign-On, specifically affecting service provider implementations in versions ranging from zero point zero point zero up through three point two point zero. This issue is classified as an open redirect or URL redirection to an untrusted site, which fundamentally undermines the integrity of the authentication flow by allowing attackers to manipulate the destination of user redirects during the SSO process. In a standard SAML architecture, the service provider relies on specific assertions and metadata from the identity provider to establish trust and authenticate users securely. However, this vulnerability introduces a mechanism where an attacker can inject malicious URLs into parameters that control post-authentication redirections or error handling paths. By exploiting this flaw, it becomes possible for external actors to fake the source of data presented to the end user, effectively creating a phishing vector disguised as legitimate authentication traffic from trusted domains associated with the Drupal site.
From a technical perspective, the root cause lies in insufficient validation and sanitization of redirect URLs provided by users or derived from SAML responses before they are processed for redirection. When the service provider accepts input that dictates where to send the user after successful login or during error states, it fails to verify whether the target domain is whitelisted or matches expected patterns. This lack of strict allow-listing permits absolute URLs pointing to external, potentially malicious domains. Consequently, an attacker can craft a specially designed SAML request or manipulate existing parameters to force the browser to redirect to a phishing site that mimics the appearance of the legitimate application. The victim, believing they are interacting with the trusted Drupal environment, may inadvertently enter credentials or sensitive information into the fraudulent page controlled by the adversary. This behavior aligns directly with CWE-601, which defines URL redirection to an untrusted site as a weakness where software redirects users to URLs provided by external sources without proper validation of trustworthiness.
The operational impact of this vulnerability is severe due to its potential for social engineering and credential harvesting. Since SAML is often used in enterprise environments with high-value assets, compromising the authentication flow can lead to unauthorized access if combined with other attacks or simply through direct phishing success. Attackers can leverage this redirect flaw to bypass security controls that rely on domain verification, such as browser-based trust indicators or corporate firewalls that might allow traffic from known internal domains but block external ones. If an attacker successfully redirects a user to a malicious site while maintaining the visual context of the original application through careful design, they can capture session cookies, passwords, or multi-factor authentication codes. This undermines the core promise of SSO, which is secure and seamless access across multiple applications without repeated logins. The ability to fake the source of data means that even if users are cautious about typing credentials into unknown sites, the visual cues provided by a convincing phishing page can deceive them, leading to significant security breaches within the organization's identity infrastructure.
To mitigate this risk, immediate action is required for all systems running vulnerable versions of the SAML SSO service provider module. The primary remediation strategy involves upgrading to a patched version that implements strict validation mechanisms for redirect URLs. Developers should enforce an allow-list approach where only explicitly trusted domains are permitted as redirection targets. Any URL not matching this list must be rejected or redirected to a safe default page, such as the application homepage. Additionally, implementing Content Security Policy headers can help mitigate some effects by restricting where scripts and frames can load from, although it does not directly prevent server-side redirects. For organizations unable to upgrade immediately due to compatibility constraints, input validation at the web server level using reverse proxy rules or Web Application Firewall configurations can serve as a temporary compensating control to block requests containing suspicious redirect parameters. Regular security audits and penetration testing focused on authentication flows are also recommended to ensure that no similar weaknesses exist in other parts of the identity management ecosystem.