CVE-2026-3217: Drupal SAML SSO XSS Vulnerability

CVE-2026-3217 Overview

CVE-2026-3217 is a Cross-Site Scripting (XSS) vulnerability affecting the Drupal SAML SSO - Service Provider module. The vulnerability stems from improper neutralization of input during web page generation, allowing attackers to inject malicious scripts into web pages viewed by other users. This security flaw can lead to session hijacking, credential theft, and unauthorized actions performed on behalf of authenticated users.

Critical Impact

Attackers can execute arbitrary JavaScript in the context of authenticated user sessions, potentially compromising SAML-based single sign-on authentication flows and stealing sensitive user credentials.

Affected Products

• Drupal SAML SSO - Service Provider versions from 0.0.0 before 3.1.3

Discovery Timeline

• 2026-03-25 - CVE CVE-2026-3217 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-3217

Vulnerability Analysis

This vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The SAML SSO - Service Provider module fails to properly sanitize user-controlled input before rendering it within web pages. This allows attackers to inject malicious scripts that execute in the context of victim browsers.

In the context of a SAML Service Provider module, XSS vulnerabilities are particularly concerning because they can target the authentication flow itself. Malicious actors could potentially intercept SAML assertions, modify authentication responses, or capture session tokens during the SSO process.

Root Cause

The root cause lies in insufficient input validation and output encoding within the SAML SSO - Service Provider module. User-supplied data is incorporated into HTML output without proper sanitization, allowing script injection. This commonly occurs in SAML implementations when processing SAML response attributes, error messages, or relay state parameters that are reflected back to users.

Attack Vector

The attack is network-based and requires user interaction to succeed. An attacker crafts a malicious URL or request containing JavaScript payload targeting the vulnerable SAML SSO component. When a victim user clicks the link or submits a manipulated form, the malicious script executes in their browser session. The attack can cross security boundaries, potentially affecting other users and applications that share the same origin.

The exploitation typically involves:

1. Identifying input fields or URL parameters processed by the SAML SSO module that are reflected in page output
2. Crafting a payload that bypasses any existing input filters
3. Delivering the malicious link to target users via phishing or social engineering
4. Capturing credentials or session tokens when the victim interacts with the crafted content

Detection Methods for CVE-2026-3217

Indicators of Compromise

• Unusual JavaScript execution patterns in browser logs related to SAML authentication endpoints
• Suspicious HTTP requests containing encoded script tags targeting SAML SSO module URLs
• User reports of unexpected redirects or prompts during SSO authentication flows
• Access logs showing requests with XSS payloads in query strings or POST parameters

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block common XSS patterns in requests to Drupal SAML endpoints
• Monitor application logs for requests containing suspicious characters such as <script>, javascript:, or encoded variants targeting /saml/ paths
• Deploy Content Security Policy (CSP) headers and monitor for CSP violation reports
• Enable browser-side XSS auditor logging and review alerts related to SAML authentication pages

Monitoring Recommendations

• Configure real-time alerting for WAF XSS rule triggers on SAML SSO endpoints
• Establish baseline behavior for SAML authentication traffic and alert on anomalies
• Monitor for new DOM elements or inline scripts being injected into SAML module pages
• Review Drupal watchdog logs for authentication-related errors or unusual activity patterns

How to Mitigate CVE-2026-3217

Immediate Actions Required

• Update the Drupal SAML SSO - Service Provider module to version 3.1.3 or later immediately
• Review access logs for evidence of exploitation attempts targeting SAML endpoints
• Implement Content Security Policy headers to restrict inline script execution
• Consider temporarily disabling the SAML SSO module if immediate patching is not possible

Patch Information

The vulnerability has been addressed in SAML SSO - Service Provider version 3.1.3. Organizations should upgrade to this version or later to remediate the XSS vulnerability. Detailed patch information is available in the Drupal Security Advisory.

To update the module, use Composer or download the patched version directly from the Drupal project page.

Workarounds

• Deploy WAF rules to filter XSS patterns in requests to SAML SSO module paths pending patch deployment
• Implement strict Content Security Policy headers to block inline script execution as a defense-in-depth measure
• Restrict access to SAML SSO endpoints to trusted IP ranges if feasible in your environment
• Enable Drupal's built-in input filtering mechanisms at their strictest settings for user-facing forms

# Configuration example
# Add Content Security Policy headers in Apache for Drupal SAML endpoints
<Location "/saml/">
    Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'"
    Header set X-XSS-Protection "1; mode=block"
    Header set X-Content-Type-Options "nosniff"
</Location>