CVE-2007-3498 in Htmlpurifier
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in smoketests/configForm.php in HTML Purifier before 2.0.1 allows remote attackers to inject arbitrary web script or HTML via unspecified vectors related to "unescaped print_r output."
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Analysis
by VulDB Data Team • 07/20/2021
The vulnerability described in CVE-2007-3498 represents a critical cross-site scripting flaw within the HTML Purifier library version 2.0.0 and earlier. This security weakness specifically affects the smoketests/configForm.php component of the application, which serves as a configuration testing interface for the HTML Purifier sanitization tool. The vulnerability arises from improper handling of user input within the print_r output functionality, creating an avenue for malicious actors to execute arbitrary web scripts or HTML code within the context of affected web applications. The issue stems from the library's failure to properly escape or sanitize data that is displayed through the print_r function, which is commonly used for debugging purposes but becomes dangerous when user-controllable data flows into it without adequate sanitization.
The technical exploitation of this vulnerability occurs through the injection of malicious payloads into parameters that are subsequently processed by the print_r function within the configuration form. When the application renders the configuration interface, the unescaped output of print_r displays user-supplied data directly to the browser without proper HTML escaping or sanitization. This creates a classic XSS vector where attackers can craft malicious input that, when processed by print_r, executes unintended JavaScript code or injects malicious HTML elements in the victim's browser. The vulnerability's classification as a CWE-79 (Cross-site Scripting) indicates it falls under the well-established category of input validation flaws that permit malicious code execution in web browsers. The attack surface is particularly concerning because the affected component is part of a configuration testing interface, meaning that even legitimate administrative users who might interact with this tool could be exposed to the vulnerability.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform various malicious activities including session hijacking, credential theft, data exfiltration, and redirection to malicious sites. Since HTML Purifier is widely used for sanitizing user-generated content in web applications, exploitation of this vulnerability could potentially compromise entire applications that rely on the library for content filtering. The vulnerability's presence in the testing interface means that even non-production environments could be compromised, potentially allowing attackers to gather information about application configurations or exploit other related vulnerabilities. This makes the impact particularly severe in enterprise environments where such testing interfaces might be accessible to unauthorized users or where the testing environment shares infrastructure with production systems. The vulnerability aligns with ATT&CK technique T1566.001 (Phishing: Spearphishing Attachment) and T1203 (Exploitation for Client Execution) as attackers could leverage this XSS flaw to deliver malicious payloads to unsuspecting users.
Organizations affected by this vulnerability should immediately upgrade to HTML Purifier version 2.0.1 or later, which contains the necessary patches to address the unescaped print_r output issue. The mitigation strategy should also include implementing proper input validation and output encoding measures throughout the application stack, particularly for any debugging or testing interfaces that handle user-supplied data. Security teams should conduct thorough code reviews to identify other potential instances where print_r or similar debugging functions might be used with untrusted input, as this vulnerability pattern could exist elsewhere in the codebase. Additionally, implementing Content Security Policy headers and proper HTTP response headers can provide additional layers of protection against XSS attacks, while regular security testing and vulnerability assessments should be conducted to identify similar issues in other components of the application ecosystem. The fix implemented in version 2.0.1 specifically addresses the root cause by ensuring that all output generated by the print_r function within the configuration interface is properly escaped and sanitized before display.