CVE-2026-15917 in Drupal
Summary
by MITRE • 08/26/2026
Improper Neutralization of Input During Web Page Generation ("Cross-site Scripting") vulnerability in Drupal Drupal core allows Cross-Site Scripting (XSS). This issue affects Drupal core versions: from 11.3.0 to 11.3.14, from 11.4.0 to 11.4.4, from 0.0.0 to 11.2.*.
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Analysis
by VulDB Data Team • 08/26/2026
The identified vulnerability represents a classic instance of Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting or XSS. This flaw is embedded within the core architecture of Drupal, specifically affecting version ranges from 0.0.0 through 11.2.*, and extending into newer releases such as versions 11.3.0 to 11.3.14 and 11.4.0 to 11.4.4. The fundamental nature of this defect lies in the application's failure to adequately sanitize or encode user-supplied input before it is rendered within an HTML context. When a web server processes requests containing malicious scripts, the Drupal core fails to distinguish between legitimate data and executable code, thereby allowing attacker-controlled content to be injected directly into the page source that is sent back to the client browser.
From a technical perspective, this vulnerability typically arises when dynamic content generated by user interactions or external inputs is inserted into the DOM without proper encoding mechanisms such as HTML entity encoding or context-aware escaping. In many CMS platforms like Drupal, various endpoints including comment forms, profile fields, or API responses may accept raw input that is subsequently displayed on public-facing pages. If the sanitization layer does not strictly enforce output encoding based on the specific context of the data insertion, scripts embedded within that input will execute in the victim's browser session. This execution occurs under the security privileges of the authenticated user and the domain origin of the Drupal site, bypassing same-origin policy protections intended to isolate web applications from each other.
The operational impact of this vulnerability is severe due to its potential for widespread exploitation by unauthenticated or low-privilege attackers. Successful exploitation allows an attacker to execute arbitrary JavaScript code in the context of the affected website. This capability enables a range of malicious activities including session hijacking, where stolen cookies and authentication tokens are exfiltrated to allow full account takeover; keylogging to capture sensitive credentials entered on the site; defacement by modifying page content for phishing or propaganda purposes; and redirection attacks that funnel users to malicious third-party sites designed to deliver malware. Because Drupal is widely used across enterprise environments, educational institutions, and government sectors, the scale of potential damage is amplified significantly if left unpatched.
This vulnerability aligns with CWE-79, which categorizes Improper Neutralization of Input During Web Page Generation as a critical weakness in web application security frameworks. Furthermore, from an offensive cybersecurity perspective, this flaw facilitates techniques documented in the MITRE ATT&CK framework under T1059, specifically Command and Scripting Interpretation via browser-based execution. The attack vector is generally classified as Remote with Low Complexity because it often requires only a single interaction such as clicking a crafted link or submitting a form containing malicious payload data. There are no complex prerequisites for exploitation beyond the ability to inject input into an affected endpoint that reflects or stores user content on subsequent page loads.
Mitigation strategies must prioritize immediate patching of all Drupal installations within the specified vulnerable version ranges. Administrators should upgrade to versions outside the identified risk windows, ensuring that the latest security patches provided by the Drupal Security Team are applied promptly. In scenarios where immediate upgrading is not feasible due to compatibility constraints or operational downtime requirements, temporary compensating controls must be implemented. These include configuring Web Application Firewalls with rulesets capable of detecting and blocking XSS payloads in HTTP request parameters and response bodies. Additionally, developers should audit custom modules and themes for similar input handling flaws, ensuring that all output escaping follows Drupal’s recommended practices using functions like Html::escape() or Twig auto-escaping features to guarantee that user data is treated strictly as text rather than executable code.