CVE-2025-14556: Drupal Flag Module XSS Vulnerability

CVE-2025-14556 Overview

CVE-2025-14556 is a Cross-Site Scripting (XSS) vulnerability affecting the Drupal Flag 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 affects Flag module versions from 7.X-3.0 through 7.X-3.9.

Critical Impact

Authenticated attackers can exploit this XSS vulnerability to execute arbitrary JavaScript in victim browsers, potentially leading to session hijacking, credential theft, or malicious content injection on affected Drupal sites.

Affected Products

• Drupal Flag module versions 7.X-3.0 through 7.X-3.9
• Backdrop CMS Flag module (related advisory)

Discovery Timeline

• 2026-01-14 - CVE-2025-14556 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2025-14556

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation). The Drupal Flag module fails to properly sanitize user-supplied input before rendering it in web pages, creating an opportunity for Cross-Site Scripting attacks.

The attack requires network access and authenticated user privileges, combined with user interaction from the victim. When successfully exploited, the vulnerability impacts the confidentiality and integrity of downstream components, though the vulnerable system itself maintains its security posture.

Root Cause

The root cause lies in insufficient input validation and output encoding within the Flag module's rendering logic. User-controllable data is incorporated into page output without adequate sanitization, allowing script injection. This is a common pattern in CMS modules where dynamic content handling does not consistently apply security filters to all user input paths.

Attack Vector

The attack is network-based, requiring an authenticated attacker with low privileges to submit malicious input through the Flag module's interface. Successful exploitation requires active user interaction—a victim must navigate to a page containing the injected payload. Once triggered, the malicious script executes within the victim's browser session context.

The exploitation flow typically involves:

1. An authenticated attacker identifies an input field in the Flag module that lacks proper sanitization
2. The attacker injects a crafted XSS payload through this input
3. When another user views content rendered with the malicious input, the script executes
4. The attacker can then steal session cookies, redirect users, or modify page content

Detection Methods for CVE-2025-14556

Indicators of Compromise

• Unexpected JavaScript code or script tags appearing in Flag module content or database fields
• Unusual network requests to external domains originating from page views on Drupal sites
• Reports from users of unexpected browser behavior or redirects when interacting with flagged content
• Web application firewall logs showing blocked XSS patterns targeting Flag module endpoints

Detection Strategies

• Deploy web application firewall (WAF) rules to detect and block common XSS payloads targeting Drupal installations
• Implement Content Security Policy (CSP) headers to restrict script execution sources and detect policy violations
• Monitor Drupal watchdog logs for suspicious input patterns or encoding anomalies in Flag module operations
• Conduct regular security audits of stored content for injected script patterns

Monitoring Recommendations

• Enable verbose logging for the Flag module to capture all user interactions and input submissions
• Configure browser-side reporting endpoints to collect CSP violation reports
• Implement real-time alerting for WAF rule triggers related to XSS attack patterns
• Review user activity logs for accounts submitting unusual content patterns

How to Mitigate CVE-2025-14556

Immediate Actions Required

• Upgrade the Drupal Flag module to a patched version beyond 7.X-3.9 when available
• Review and audit existing flagged content for potential injected scripts or malicious code
• Implement strict Content Security Policy headers to limit script execution capabilities
• Consider temporarily disabling the Flag module if critical and no patch is available

Patch Information

Security advisories have been published by Tag1 and HeroDevs. Administrators should consult these resources for the latest patch information and upgrade instructions. For sites running end-of-life Drupal 7, extended support options may be available through vendors like HeroDevs.

Workarounds

• Implement server-side input validation to strip or encode potentially dangerous characters before storage
• Deploy a web application firewall with XSS protection rules in front of the Drupal installation
• Restrict user permissions to minimize the number of accounts capable of creating or modifying flagged content
• Apply Content Security Policy headers with strict script-src directives to prevent inline script execution

# Apache .htaccess CSP header configuration example
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';"