CVE-2015-8936 in squidGuard
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in squidGuard.cgi in squidGuard before 1.5 allows remote attackers to inject arbitrary web script or HTML via a blocked site link.
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Analysis
by VulDB Data Team • 11/04/2024
The vulnerability identified as CVE-2015-8936 represents a critical cross-site scripting flaw in the squidGuard web interface component known as squidGuard.cgi. This vulnerability affects squidGuard versions prior to 1.5 and exposes systems to remote code execution through malicious web script injection. The flaw exists within the handling of blocked site links, where user-supplied input is not properly sanitized before being rendered in the web interface. This allows attackers to craft malicious URLs that, when clicked by victims, execute arbitrary JavaScript code within the context of the victim's browser session. The vulnerability specifically impacts the squidGuard web administration interface which is commonly used in proxy server configurations to filter and block access to certain websites based on predefined rules.
The technical implementation of this XSS vulnerability stems from improper input validation and output encoding practices within the squidGuard.cgi script. When the web interface processes blocked site links, it fails to properly escape or sanitize user-provided data before incorporating it into HTML output. This creates an environment where attacker-controlled content can be injected directly into the web page structure, enabling malicious scripts to execute in the victim's browser context. The vulnerability is classified as a classic reflected XSS attack pattern where the malicious payload is embedded in a URL and executed when the user accesses the malicious link. According to CWE standards, this maps to CWE-79 which describes improper neutralization of input during web page generation, specifically in the context of web applications that generate dynamic content without proper sanitization.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform session hijacking, steal sensitive authentication tokens, redirect users to malicious websites, or execute more sophisticated attacks through the victim's browser. In proxy server environments where squidGuard is deployed for content filtering, this vulnerability could allow attackers to bypass security controls and access restricted content, or to manipulate the proxy's filtering behavior. The attack vector is particularly dangerous because it requires minimal user interaction beyond clicking a malicious link, making it effective in phishing campaigns or social engineering attacks. Organizations using squidGuard for network security enforcement are particularly vulnerable as this flaw undermines the very purpose of content filtering and access control mechanisms. The vulnerability also aligns with ATT&CK technique T1059.007 which covers scripting languages including JavaScript, and T1566 which covers spearphishing attacks that often leverage XSS vulnerabilities to deliver malicious payloads.
Mitigation strategies for CVE-2015-8936 should prioritize immediate patching of squidGuard installations to version 1.5 or later where the vulnerability has been addressed through proper input sanitization and output encoding. Organizations should also implement additional defensive measures including web application firewalls that can detect and block malicious script injection attempts, proper input validation at all application entry points, and regular security auditing of web interfaces. Network administrators should consider implementing additional monitoring for suspicious traffic patterns that might indicate exploitation attempts, while also ensuring that access to the squidGuard web interface is restricted to authorized personnel only. The vulnerability highlights the importance of proper security practices in web application development, particularly around input validation and output encoding, which are fundamental principles in preventing XSS attacks according to OWASP top ten security risks and industry best practices for secure coding.