CVE-2002-0535 in Postnuke
Summary
by MITRE
Cross-site scripting vulnerabilities in PostBoard 2.0.1 and earlier allows remote attackers to execute script as other users via (1) an [IMG] tag when BBCode is enabled, or (2) in a topic title.
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Analysis
by VulDB Data Team • 09/16/2025
The vulnerability identified as CVE-2002-0535 represents a critical cross-site scripting flaw affecting PostBoard versions 2.0.1 and earlier. This security weakness resides in the application's handling of user input within bulletin board systems, specifically when BBCode functionality is enabled. The vulnerability manifests through two distinct attack vectors that collectively enable malicious actors to inject and execute arbitrary scripts in the context of other users' browsers. The first vector exploits the [IMG] tag functionality when BBCode is enabled, allowing attackers to craft malicious image tags that contain embedded script code. The second vector targets topic titles, where similar scripting attacks can be executed through carefully crafted input that bypasses normal sanitization measures. This vulnerability directly violates the fundamental security principle of input validation and demonstrates a failure to properly sanitize user-supplied content before rendering it within web pages.
The technical implementation of this vulnerability stems from inadequate sanitization of user input within the PostBoard application's rendering engine. When BBCode is enabled, the system processes [IMG] tags without sufficient validation of the src attribute content, allowing attackers to inject malicious javascript code within the image source parameter. The topic title vulnerability occurs because the application fails to properly escape or filter special characters in user-generated content before displaying it in HTML contexts. Both attack vectors exploit the browser's interpretation of HTML content, where script tags or javascript execution contexts can be embedded within legitimate-looking elements. This flaw aligns with CWE-79, which specifically addresses cross-site scripting vulnerabilities in web applications. The vulnerability's exploitation requires minimal technical skill and can be accomplished through standard web application attack techniques, making it particularly dangerous in public bulletin board environments where users trust the platform's content.
The operational impact of CVE-2002-0535 extends beyond simple script execution, as it enables attackers to perform session hijacking, steal cookies, redirect users to malicious sites, and potentially gain unauthorized access to user accounts. When users view infected topics or images, their browsers execute the embedded scripts, which can capture session tokens, redirect to phishing sites, or perform actions on behalf of the authenticated user. The vulnerability affects all users of the affected PostBoard versions, making it particularly concerning for public forums where many users may be logged in with administrative privileges. Attackers can leverage this vulnerability to compromise entire user bases, especially in environments where users trust forum content implicitly. The long-term impact includes potential data breaches, loss of user trust, and reputational damage to organizations hosting vulnerable bulletin board systems. This vulnerability also demonstrates weaknesses in the application's defense-in-depth strategy, as it fails to implement proper output encoding and input validation mechanisms.
Mitigation strategies for CVE-2002-0535 require immediate implementation of multiple security controls. Organizations should upgrade to PostBoard versions that address this vulnerability, as the original affected versions lack proper sanitization mechanisms. The primary technical fix involves implementing comprehensive input validation and output encoding for all user-supplied content, particularly when BBCode or HTML rendering is enabled. The application should sanitize image source attributes by validating URLs and rejecting potentially malicious content, while also implementing proper HTML escaping for all dynamic content including topic titles. Security measures should include the implementation of Content Security Policy headers to prevent script execution, and the use of strict input validation libraries that can identify and neutralize malicious payloads. Additionally, administrators should disable BBCode functionality when not required, as this reduces the attack surface. The remediation process should follow ATT&CK framework guidance for mitigating web application vulnerabilities, specifically focusing on techniques related to input validation and output encoding. Regular security testing including dynamic application security testing and manual penetration testing should be conducted to ensure the effectiveness of implemented controls and to identify potential new vulnerabilities in similar systems.