CVE-2009-4408 in PyForum
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in models.parser in PyForum 1.0.3 and possibly earlier versions, and possibly zForum, allow remote attackers to inject arbitrary web script or HTML via crafted BBcode (1) img or (2) url tags, which are not properly handled when a post is viewed.
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Analysis
by VulDB Data Team • 01/25/2019
The vulnerability identified as CVE-2009-4408 represents a critical cross-site scripting flaw affecting PyForum 1.0.3 and potentially earlier versions, with similar risks present in zForum applications. This issue stems from inadequate input validation and sanitization mechanisms within the BBcode processing functionality, specifically targeting the img and url tag handlers within the models.parser component. The vulnerability manifests when maliciously crafted BBcode elements are submitted through forum posts and subsequently rendered without proper security measures, creating an avenue for remote attackers to execute arbitrary web scripts or HTML code within the context of other users' browsers.
The technical exploitation of this vulnerability occurs through the manipulation of BBcode tags that are commonly used for embedding images and hyperlinks within forum environments. When an attacker submits a post containing maliciously crafted img or url BBcode tags, the application fails to properly sanitize these inputs before rendering them in the user interface. This processing gap creates a persistent XSS vector where the malicious code becomes part of the rendered content and executes whenever other users view the affected posts. The vulnerability's impact is amplified by the fact that BBcode is typically treated as a safe formatting language, leading to insufficient security checks and allowing attackers to bypass normal input validation procedures.
The operational consequences of this vulnerability extend beyond simple script execution, as it enables attackers to perform various malicious activities including session hijacking, credential theft, and redirection to malicious websites. Users who view affected posts become unwitting participants in the attack, with their browser sessions potentially compromised and their personal data exposed to unauthorized access. The persistent nature of the vulnerability means that once malicious content is posted, it continues to affect users until the content is manually removed or the application is patched, creating ongoing security risks for forum administrators and their communities.
Security mitigations for this vulnerability require immediate implementation of comprehensive input sanitization and output encoding mechanisms within the BBcode processing pipeline. The primary solution involves implementing strict validation of all BBcode parameters, particularly those used in img and url tags, ensuring that any potentially dangerous characters or sequences are properly escaped or removed before rendering. Organizations should implement Content Security Policy headers to prevent execution of unauthorized scripts and establish robust input filtering mechanisms that validate all user-submitted content against established security standards. This vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and represents a clear violation of the principle of least privilege in web application security. The attack vector follows patterns consistent with ATT&CK technique T1566.001 for initial access through malicious web content, making this vulnerability particularly dangerous in community-driven forums where user-generated content is prevalent and security controls may be insufficiently enforced.