CVE-2024-37383: Roundcube Webmail XSS Vulnerability

CVE-2024-37383 Overview

CVE-2024-37383 is a Cross-Site Scripting (XSS) vulnerability affecting Roundcube Webmail versions before 1.5.7 and 1.6.x versions before 1.6.7. The vulnerability exists in the way Roundcube handles SVG animate attributes, allowing attackers to inject malicious scripts through specially crafted email content. When a user views a malicious email, the embedded JavaScript can execute within the context of the user's session.

Critical Impact

This vulnerability is actively exploited in the wild and has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog. Attackers can steal session cookies, capture credentials, or perform actions on behalf of authenticated users accessing Roundcube webmail.

Affected Products

• Roundcube Webmail versions before 1.5.7
• Roundcube Webmail versions 1.6.x before 1.6.7
• Debian Linux 10.0 (with vulnerable Roundcube packages)

Discovery Timeline

• 2024-06-07 - CVE-2024-37383 published to NVD
• 2025-10-31 - Last updated in NVD database

Technical Details for CVE-2024-37383

Vulnerability Analysis

This XSS vulnerability stems from improper input sanitization in Roundcube's HTML washer component, specifically in how it processes SVG animate element attributes. The HTML sanitizer is designed to strip dangerous content from incoming emails to prevent XSS attacks, but the implementation failed to properly handle whitespace in attribute values when checking SVG elements.

The vulnerability allows attackers to bypass the sanitization logic by including leading or trailing whitespace in SVG animate attribute values. When the sanitizer compares attribute values to determine if they should be filtered, the whitespace causes the comparison to fail, allowing malicious attributes to pass through unfiltered. This enables injection of JavaScript code that executes when the email is rendered in the victim's browser.

Root Cause

The root cause lies in the rcube_washtml.php file, which handles HTML sanitization. The attribute value comparison function did not trim whitespace from attribute values before performing the security check. This allowed attackers to pad malicious attribute values with spaces, bypassing the sanitizer's allowlist checks while still having the JavaScript execute when rendered by the browser.

Attack Vector

The attack is network-based and requires user interaction. An attacker sends a specially crafted email containing an SVG element with malicious animate attributes padded with whitespace. When the victim opens or previews the email in Roundcube, the JavaScript payload executes in their browser session. This can lead to session hijacking, credential theft, or further phishing attacks conducted from the compromised user's context.

// Security patch from rcube_washtml.php
// Source: https://github.com/roundcube/roundcubemail/commit/43aaaa528646877789ec028d87924ba1accf5242
 
        foreach ($node->attributes as $name => $attr) {
            if (strtolower($name) === $attr_name) {
-                if (strtolower($attr_value) === strtolower($attr->nodeValue)) {
+                if (strtolower($attr_value) === strtolower(trim($attr->nodeValue))) {
                    return true;
                }
            }

The fix adds the trim() function to normalize attribute values before comparison, ensuring whitespace-padded malicious values are properly detected and filtered.

Detection Methods for CVE-2024-37383

Indicators of Compromise

• Incoming emails containing SVG elements with animate, animateTransform, or animateMotion tags
• Email content with unusual whitespace patterns in SVG attribute values
• Web server logs showing unusual JavaScript execution or external resource loading after email access
• User reports of unexpected browser behavior when viewing emails

Detection Strategies

• Implement web application firewall (WAF) rules to inspect email content for SVG animate elements with suspicious attributes
• Monitor browser console logs for JavaScript errors or unexpected script execution during webmail sessions
• Review Roundcube access logs for patterns indicating XSS exploitation attempts
• Deploy endpoint detection solutions to identify suspicious browser activity following webmail interaction

Monitoring Recommendations

• Enable verbose logging for Roundcube webmail to capture detailed request/response data
• Configure SIEM alerts for detection of SVG-based payload patterns in email traffic
• Monitor network traffic for data exfiltration attempts following email viewing activity
• Implement Content Security Policy (CSP) reporting to detect inline script execution attempts

How to Mitigate CVE-2024-37383

Immediate Actions Required

• Upgrade Roundcube Webmail to version 1.5.7 or later for the 1.5.x branch
• Upgrade Roundcube Webmail to version 1.6.7 or later for the 1.6.x branch
• Review server logs for evidence of exploitation attempts targeting this vulnerability
• Consider temporarily disabling HTML email rendering until patches are applied

Patch Information

Roundcube has released patched versions addressing this vulnerability. Organizations should upgrade to Roundcube Webmail 1.5.7 or 1.6.7 depending on their current version branch. The security fix is contained in commit 43aaaa528646877789ec028d87924ba1accf5242.

For Debian Linux 10.0 users, refer to the Debian LTS Security Announcement for package update instructions. Additional details are available in the Roundcube 1.5.7 Release Notes and Roundcube 1.6.7 Release Notes.

Workarounds

• Configure email clients to display emails in plain text mode only until the patch is applied
• Implement strict Content Security Policy (CSP) headers to mitigate JavaScript execution risks
• Deploy a web application firewall with rules to strip or block SVG elements in incoming email content
• Restrict webmail access to trusted networks until remediation is complete

# Example: Apply strict CSP headers in Apache configuration
# Add to Roundcube's .htaccess or virtual host configuration
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'none';"