CVE-2006-0195 in SquirrelMail
Summary
by MITRE
Interpretation conflict in the MagicHTML filter in SquirrelMail 1.4.0 to 1.4.5 allows remote attackers to conduct cross-site scripting (XSS) attacks via style sheet specifiers with invalid (1) "/*" and "*/" comments, or (2) a newline in a "url" specifier, which is processed by certain web browsers including Internet Explorer.
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Analysis
by VulDB Data Team • 06/14/2019
The vulnerability CVE-2006-0195 represents a critical interpretation conflict within the MagicHTML filter component of SquirrelMail versions 1.4.0 through 1.4.5, exposing systems to cross-site scripting attacks. This flaw stems from improper handling of CSS style sheet specifiers in the HTML filtering mechanism, creating a pathway for malicious actors to inject harmful code into web applications. The vulnerability specifically targets the processing of CSS comments and URL specifiers, leveraging browser-specific parsing behaviors to bypass security controls. The MagicHTML filter was designed to sanitize HTML content and prevent malicious code execution, but this implementation flaw created a significant security gap that attackers could exploit.
The technical implementation of this vulnerability occurs when the MagicHTML filter encounters CSS style sheet specifiers containing invalid comment sequences or newline characters within URL specifiers. When processing CSS content with the sequence "/" followed by "/" comments, certain web browsers including Internet Explorer interpret these sequences differently than the filter expects, allowing malicious code to be injected. Additionally, when a newline character appears within a "url" specifier, the browser's CSS parser may process the content in a manner that bypasses the filter's sanitization logic. This interpretation conflict creates a scenario where legitimate CSS parsing behavior becomes a vector for XSS exploitation, particularly affecting Internet Explorer's rendering engine which has specific handling for these edge cases. The vulnerability operates at the intersection of HTML sanitization and CSS parsing, where the filter's assumptions about how CSS should be processed conflict with actual browser behavior.
The operational impact of this vulnerability is significant for organizations using affected SquirrelMail versions, as it enables remote attackers to execute arbitrary JavaScript code within the context of users' browsers. This allows for session hijacking, credential theft, data exfiltration, and other malicious activities that can compromise the entire web application and user data. The vulnerability affects any user who receives email messages containing maliciously crafted HTML content, making it particularly dangerous in environments where users frequently access email from untrusted sources. The attack vector is particularly concerning because it leverages the inherent behavior of web browsers rather than requiring complex exploitation techniques, making it accessible to attackers with minimal technical expertise. The vulnerability also demonstrates the complexity of HTML sanitization in web applications, where the interaction between different parsing engines and security controls can create unexpected attack surfaces.
Organizations should immediately upgrade to SquirrelMail versions 1.4.6 or later, which contain patches addressing this specific interpretation conflict in the MagicHTML filter. System administrators should implement additional security measures including content security policies, proper input validation, and regular security assessments of web applications. The vulnerability aligns with CWE-79, which describes cross-site scripting flaws, and relates to ATT&CK technique T1566 for spearphishing attacks that could leverage this vulnerability. Additional mitigations include implementing web application firewalls, restricting email content filtering, and educating users about the risks of opening suspicious emails. The incident highlights the importance of thorough testing of security controls against browser-specific behaviors and the need for comprehensive security assessments that consider the interaction between different parsing engines and security mechanisms. Organizations should also consider implementing multi-factor authentication and other protective measures to reduce the potential impact of successful exploitation attempts.