CVE-2018-3735 in bracket-template
Summary
by MITRE
bracket-template suffers from reflected XSS possible when variable passed via GET parameter is used in template
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Analysis
by VulDB Data Team • 02/17/2020
The vulnerability identified as CVE-2018-3735 affects the bracket-template library, which is commonly used for template processing in web applications. This issue represents a classic reflected cross-site scripting vulnerability that occurs when user-supplied data is not properly sanitized before being rendered within template contexts. The flaw manifests when GET parameters are passed directly into template variables without adequate input validation or output encoding, creating an avenue for malicious actors to inject arbitrary JavaScript code that executes in the context of other users' browsers.
The technical root cause of this vulnerability stems from insufficient sanitization of user input within the template rendering pipeline. When a web application processes a GET request containing malicious payloads and subsequently incorporates that data into a template without proper escaping mechanisms, the template engine treats the injected code as executable JavaScript rather than plain text. This allows attackers to construct malicious URLs that, when visited by victims, trigger the execution of harmful scripts in the victim's browser context. The vulnerability is categorized under CWE-79 as "Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')", which specifically addresses the failure to properly encode or escape output that originates from untrusted sources.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, deface web applications, steal sensitive user data, or redirect victims to malicious sites. Attackers can craft payloads that exploit the reflected XSS to capture cookies, modify page content, or even perform actions on behalf of authenticated users. The vulnerability is particularly dangerous in environments where the template engine processes sensitive user data or where administrative functions are exposed through template variables, as it could potentially allow privilege escalation or unauthorized access to protected resources. This type of vulnerability is classified under the ATT&CK framework as T1059.008 - "Command and Scripting Interpreter: PowerShell" or more broadly T1566 - "Phishing" when used in conjunction with social engineering tactics.
Mitigation strategies for CVE-2018-3735 involve implementing comprehensive input validation and output encoding mechanisms throughout the template processing pipeline. Developers should ensure that all user-supplied data is properly escaped before being rendered in template contexts, with particular attention to HTML, JavaScript, and URL encoding based on the specific output context. The recommended approach includes implementing Content Security Policy headers to limit script execution, utilizing template engines that automatically escape output by default, and conducting regular security reviews of template usage patterns. Additionally, organizations should implement proper parameter validation, employ web application firewalls to detect and block malicious payloads, and maintain up-to-date dependencies to ensure that known vulnerabilities are patched. The vulnerability demonstrates the critical importance of following secure coding practices and input sanitization principles, particularly when dealing with dynamic content generation in web applications.