CVE-2007-0399 in Simple Machines Forum
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in index.php in Simple Machines Forum (SMF) 1.1 RC3 allow remote authenticated users to inject arbitrary web script or HTML via the (1) recipient or (2) BCC field when selecting send in a pm action.
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Analysis
by VulDB Data Team • 12/26/2025
The vulnerability identified as CVE-2007-0399 affects Simple Machines Forum version 1.1 RC3 and represents a critical cross-site scripting flaw that enables authenticated users to execute malicious code within the context of other users' browsers. This vulnerability specifically targets the private messaging functionality of the forum software, creating a pathway for attackers to exploit the application's input validation mechanisms. The issue stems from inadequate sanitization of user-provided data in the recipient and BCC fields during private message composition, allowing malicious scripts to be injected and subsequently executed when other users view these messages.
The technical nature of this vulnerability aligns with CWE-79, which describes cross-site scripting flaws where untrusted data is incorporated into web pages without proper validation or encoding. The vulnerability operates through a classic reflected XSS attack vector, where the malicious input is processed by the server and then reflected back to the victim's browser in the context of a legitimate request. In this case, the flaw exists in the index.php file which handles the private messaging functionality, making it particularly dangerous as it leverages the trust relationship between users within the forum environment.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to steal session cookies, redirect users to malicious websites, or perform actions on behalf of victims within the forum context. Since the vulnerability requires authentication, it represents a privilege escalation risk that could allow attackers to manipulate the forum's user base or compromise sensitive information shared through private messaging. The attack vector specifically targets the pm action functionality, making it particularly insidious as it can be triggered during routine forum operations, potentially going unnoticed by administrators.
Mitigation strategies for this vulnerability should include immediate implementation of input validation and output encoding mechanisms, specifically targeting the recipient and BCC fields in private messaging functionality. Organizations should deploy proper HTML entity encoding for all user-generated content before rendering it in web pages, following the principles outlined in the OWASP XSS Prevention Cheat Sheet. Additionally, implementing Content Security Policy headers can provide an additional layer of protection against script execution. The vulnerability also highlights the importance of regular security audits and input validation testing, as emphasized in the NIST Cybersecurity Framework and aligned with ATT&CK technique T1211 for exploiting vulnerabilities in web applications. Given the age of this vulnerability, organizations should prioritize upgrading to supported versions of SMF or implementing comprehensive patch management procedures to address similar issues in other forum software.