CVE-2007-6321 in RoundCube Webmail
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in RoundCube webmail 0.1rc2, 2007-12-09, and earlier versions, when using Internet Explorer, allows remote attackers to inject arbitrary web script or HTML via style sheets containing expression commands.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 12/08/2025
The vulnerability identified as CVE-2007-6321 represents a critical cross-site scripting flaw in RoundCube webmail versions 0.1rc2 and earlier, specifically manifesting when the application processes style sheets containing expression commands within Internet Explorer browsers. This vulnerability resides in the web application's improper input validation and output encoding mechanisms, creating an exploitable condition that enables remote attackers to inject malicious code into web pages viewed by other users. The flaw demonstrates characteristics consistent with CWE-79, which describes improper neutralization of input during web page generation, specifically in the context of client-side script injection.
The technical exploitation occurs through the manipulation of Cascading Style Sheets that contain expression commands, a feature supported by Internet Explorer but not by other modern browsers. When RoundCube processes user-supplied data that gets rendered within style sheet contexts, the application fails to properly sanitize or encode special characters that could trigger script execution within the browser environment. Attackers can craft malicious inputs containing expressions such as expression(alert(1)) or similar constructs that will execute arbitrary JavaScript code when the affected web page renders in Internet Explorer. This particular variant of XSS demonstrates the dangers of browser-specific features that can be leveraged for malicious purposes, as the vulnerability is specifically tied to Internet Explorer's handling of CSS expressions rather than generic HTML injection.
The operational impact of this vulnerability extends beyond simple script injection, as it enables attackers to perform a wide range of malicious activities including session hijacking, credential theft, redirection to malicious sites, and data exfiltration from authenticated users. In a webmail environment, this represents a severe threat since RoundCube applications typically handle sensitive user communications and personal data. The vulnerability affects all users who access the webmail interface through Internet Explorer, making it particularly dangerous in corporate environments where legacy browser support is maintained. The attack vector is particularly insidious because it requires minimal user interaction beyond visiting a compromised page, and the malicious code executes automatically within the victim's browser context, leveraging the existing trust relationship between the user and the webmail application.
Security professionals should implement comprehensive mitigations including immediate patching of RoundCube installations to versions that address this vulnerability, along with implementing proper input validation and output encoding mechanisms. The fix should include sanitization of user-supplied data before rendering within CSS contexts, and implementation of Content Security Policy headers to prevent unauthorized script execution. Additionally, organizations should consider browser compatibility strategies that discourage use of legacy Internet Explorer versions, as these browsers are increasingly vulnerable to such attacks. This vulnerability aligns with ATT&CK technique T1059.007 for JavaScript execution and demonstrates the importance of proper input validation as outlined in OWASP Top 10 2021 category A03: Injection, specifically addressing the need for robust sanitization of all user-controllable inputs in web applications.