CVE-2026-87953 in SAML SSO
Summary
by MITRE • 10/22/2026
Server-Side Request Forgery (SSRF) vulnerability in Drupal SAML SSO - Service Provider allows Server Side Request Forgery. 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 server-side request forgery flaw within the Drupal module for SAML Single Sign-On acting as a service provider, specifically impacting version ranges from initial release up through 3.2.0. This security defect arises when the application processes user-supplied input to construct outbound network requests without adequate validation or sanitization of the target destination. In this context, an attacker can manipulate parameters that dictate where the server should send authentication-related HTTP traffic, effectively forcing the backend system to initiate connections to arbitrary internal or external resources under the identity and privileges of the web application itself. This misconfiguration allows for unauthorized access to sensitive infrastructure components that are typically shielded from direct internet exposure by firewalls or network segmentation policies.
From a technical perspective, this vulnerability is classified as CWE-918, which defines server-side request forgery where an attacker influences the server to make requests on their behalf. The root cause lies in the insufficient validation of URL parameters passed during the SAML authentication flow. When the service provider initiates communication with identity providers or other backend services, it fails to enforce a strict allowlist of permitted domains or IP ranges. Consequently, malicious actors can inject payloads containing internal URLs pointing to localhost addresses, cloud metadata endpoints such as AWS EC2 instance metadata service at 169.254.169.254, or private network segments accessible only from the application server. This capability transforms a standard authentication module into a powerful proxy for probing and exploiting internal network architectures.
The operational impact of this vulnerability is severe, as it facilitates reconnaissance and potential data exfiltration within an organization's trusted environment. Attackers can leverage SSRF to scan internal ports, identify running services on private networks, or access sensitive configuration files stored locally on the server. Furthermore, by targeting cloud metadata endpoints, adversaries may retrieve temporary security credentials, IAM roles, and other confidential instance-specific data that could lead to full compromise of associated cloud resources. This aligns with MITRE ATT&CK technique T1557, which covers Adversary-in-the-Middle scenarios where the attacker intercepts or manipulates communication between two parties, although in this specific SSRF case, it more directly relates to lateral movement and discovery phases by using the compromised web server as a pivot point.
Mitigation strategies must prioritize immediate remediation through software updates alongside robust architectural controls. The primary defense is upgrading the Drupal SAML SSO module to version 3.2.1 or later, where developers have implemented stricter input validation mechanisms that reject requests targeting non-whitelisted hosts. In addition to patching, organizations should implement network-level protections such as egress filtering rules on firewalls and web application firewalls to block outbound connections from the web server tier to internal IP ranges unless explicitly required for business logic. Utilizing a proxy with strict allowlisting capabilities can also prevent direct access to sensitive endpoints. Regular security audits focusing on input validation patterns in all modules handling external communications are essential to maintain resilience against similar SSRF vectors across the Drupal ecosystem.