CVE-2016-7571 in Drupal
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Drupal 8.x before 8.1.10 allows remote attackers to inject arbitrary web script or HTML via vectors involving an HTTP exception.
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Analysis
by VulDB Data Team • 09/22/2022
The CVE-2016-7571 vulnerability represents a critical cross-site scripting flaw discovered in Drupal 8.x versions prior to 8.1.10, demonstrating a significant weakness in the content management system's input validation and output escaping mechanisms. This vulnerability specifically manifests when the application encounters HTTP exceptions during processing, creating an attack surface where malicious actors can inject arbitrary web scripts or HTML content into the application's response. The flaw exploits the improper handling of exception messages that contain user-supplied data without adequate sanitization, allowing attackers to execute malicious code within the context of a victim's browser session. This type of vulnerability falls under the CWE-79 category of Cross-Site Scripting, which is classified as a fundamental web application security weakness that has been consistently identified as one of the most prevalent and dangerous vulnerabilities in web applications. The vulnerability is particularly concerning because it affects the core exception handling mechanism of Drupal 8, which is invoked during normal application operation when unexpected HTTP errors occur, making it difficult for administrators to predict or prevent exploitation.
The technical exploitation of this vulnerability occurs when an attacker can manipulate HTTP request parameters or trigger specific HTTP exceptions within the Drupal 8 framework, causing the system to render user-supplied data directly into HTML output without proper encoding or sanitization. When the application processes an HTTP exception and displays error messages containing unescaped input data, malicious scripts embedded within the exception context can be executed by the victim's browser. The attack vector leverages the fact that Drupal 8's default error handling does not sufficiently escape special characters or HTML entities in exception messages, particularly when these messages contain data from HTTP request parameters or other user-controlled inputs. This vulnerability is particularly dangerous because it operates at the framework level rather than in individual modules, meaning that successful exploitation can potentially affect all components of the Drupal 8 installation. The flaw is categorized under ATT&CK technique T1203 - Exploitation for Client Execution, which describes how attackers can use vulnerabilities to execute malicious code in the context of the victim's browser.
The operational impact of CVE-2016-7571 extends beyond simple script injection, as it can enable attackers to perform a wide range of malicious activities including session hijacking, data theft, defacement of web content, and redirection to malicious websites. An attacker who successfully exploits this vulnerability could potentially steal administrator credentials, modify website content, or establish persistent backdoors within the Drupal installation. The vulnerability's remote nature means that attackers do not require local access to the server and can exploit it from anywhere on the internet, making it particularly dangerous for publicly accessible Drupal websites. Organizations running affected versions of Drupal 8 are at risk of having their websites compromised, which could result in significant reputational damage, regulatory penalties, and financial losses. The vulnerability affects not just the web application itself but also the users who interact with the compromised site, potentially exposing them to further attacks or data breaches. Given that Drupal 8 was designed with security in mind and included various protections against common web vulnerabilities, this flaw represented a significant regression in the application's security posture and highlighted the importance of thorough testing of core framework components.
Mitigation strategies for CVE-2016-7571 primarily involve immediate patching of affected Drupal 8 installations to version 8.1.10 or later, which includes the necessary fixes to properly escape exception messages and prevent XSS injection. Organizations should also implement additional defensive measures such as web application firewalls, input validation rules, and regular security audits to detect and prevent similar vulnerabilities. The vulnerability underscores the importance of maintaining up-to-date software versions and following security best practices including the principle of least privilege, regular security assessments, and proper input sanitization. System administrators should also consider implementing Content Security Policy headers and other browser-based protections to limit the impact of potential XSS attacks. Organizations should conduct thorough testing of patched versions to ensure that security updates do not introduce regressions in functionality while also monitoring for any signs of exploitation attempts or compromise within their Drupal installations. The incident serves as a reminder of the critical importance of timely security patch management and the need for comprehensive security monitoring across all web application components, particularly those handling user input and error conditions.