CVE-2008-3773 in vBulletin
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in vBulletin 3.7.2 PL1 and 3.6.10 PL3, when "Show New Private Message Notification Pop-Up" is enabled, allows remote authenticated users to inject arbitrary web script or HTML via a private message subject (aka newpm[title]).
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 11/10/2025
This cross-site scripting vulnerability exists in vBulletin versions 3.7.2 PL1 and 3.6.10 PL3 where the application fails to properly sanitize user input in the private message subject field when the "Show New Private Message Notification Pop-Up" feature is enabled. The flaw occurs because the application does not adequately filter or escape special characters in the newpm[title] parameter before rendering it in the browser context. This allows authenticated attackers who can send private messages to inject malicious scripts that execute in the context of other users' browsers when they view the notification pop-up.
The technical implementation of this vulnerability stems from improper input validation and output encoding practices within the vBulletin application's message handling system. When a user sends a private message with a specially crafted subject line containing malicious script code, the application stores this input without sufficient sanitization. Upon receiving a notification about the new private message, the system displays the subject line in a pop-up window without proper HTML escaping, creating an XSS vector that can be exploited by attackers. This vulnerability is classified as CWE-79 - Improper Neutralization of Input During Web Page Generation, which represents one of the most common web application security flaws.
The operational impact of this vulnerability is significant as it allows attackers to execute arbitrary code in the browsers of other users who receive the malicious private messages. An attacker could potentially steal session cookies, redirect users to malicious websites, deface forums, or perform actions on behalf of other users within the context of the vulnerable application. Since the vulnerability requires only authenticated access to send private messages, it can be exploited by any registered user, making it particularly dangerous in community-driven platforms where users trust each other. This weakness also aligns with ATT&CK technique T1566.001 - Phishing: Spearphishing Attachment, as it enables attackers to craft malicious messages that appear legitimate while containing embedded payloads.
Mitigation strategies for this vulnerability include implementing proper input sanitization and output encoding mechanisms, specifically ensuring that all user-provided content in message subjects undergoes HTML escaping before being rendered in pop-up notifications. Organizations should also consider disabling the notification pop-up feature if it's not essential, as this would eliminate the attack surface. Additionally, regular security updates and patch management processes are critical, as this vulnerability was addressed in subsequent vBulletin releases. The fix typically involves implementing strict validation of the newpm[title] parameter to reject or sanitize potentially dangerous characters and ensuring that all user-generated content is properly escaped before display in web contexts. This vulnerability demonstrates the importance of defense-in-depth approaches that combine multiple security controls including input validation, output encoding, and privilege separation to prevent such persistent XSS flaws in web applications.