CVE-2017-6927 in Drupal
Summary
by MITRE
Drupal 8.4.x versions before 8.4.5 and Drupal 7.x versions before 7.57 has a Drupal.checkPlain() JavaScript function which is used to escape potentially dangerous text before outputting it to HTML (as JavaScript output does not typically go through Twig autoescaping). This function does not correctly handle all methods of injecting malicious HTML, leading to a cross-site scripting vulnerability under certain circumstances. The PHP functions which Drupal provides for HTML escaping are not affected.
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Analysis
by VulDB Data Team • 02/10/2023
The vulnerability described in CVE-2017-6927 represents a critical cross-site scripting weakness in the Drupal content management system that affects multiple version ranges including Drupal 8.4.x before 8.4.5 and Drupal 7.x before 7.57. This issue specifically targets the Drupal.checkPlain() JavaScript function which serves as a client-side HTML escaping mechanism designed to protect against malicious input during output rendering. The vulnerability stems from insufficient handling of various injection methods that can bypass the escaping logic, creating potential attack vectors for malicious actors to execute unauthorized scripts within users' browsers.
The technical flaw resides in the JavaScript implementation of the checkPlain function which fails to properly sanitize all possible methods of HTML injection. While the PHP-based HTML escaping functions within Drupal remain unaffected, the JavaScript component demonstrates inadequate protection against sophisticated XSS attack techniques. This discrepancy creates a security gap where malicious input can successfully bypass client-side validation and execute within the browser context of unsuspecting users. The vulnerability is particularly concerning because it operates at the JavaScript level where traditional server-side security measures may not fully apply, making it more challenging to detect and prevent.
The operational impact of this vulnerability extends beyond simple script execution as it can enable attackers to perform a wide range of malicious activities including session hijacking, credential theft, and data exfiltration. Users interacting with vulnerable Drupal installations may be exposed to persistent XSS attacks that can compromise their browser sessions and potentially lead to full system compromise. The vulnerability affects any user who can influence content that gets processed through the checkPlain function, making it particularly dangerous in environments where user-generated content is permitted or where administrators process untrusted input. Attackers can leverage this weakness to inject malicious scripts that execute in the context of other users' browsers, potentially gaining access to sensitive information or performing unauthorized actions on behalf of victims.
Security practitioners should implement immediate mitigation strategies including upgrading to the patched versions of Drupal 8.4.5 or Drupal 7.57 which contain the necessary fixes for the checkPlain function. Additionally, organizations should review their content management practices to minimize user input that could potentially bypass security controls. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and represents a technique commonly categorized under ATT&CK tactic TA0001 (Initial Access) through malicious code delivery. Organizations should also consider implementing additional security controls such as Content Security Policy headers and regular security auditing of JavaScript functions to prevent similar vulnerabilities from emerging in other components of their web applications.