CVE-2026-26079
📋 TL;DR
This CVE allows CSS injection in Roundcube Webmail due to improper handling of comments. Attackers can inject malicious CSS styles that could lead to UI manipulation or data exfiltration. All Roundcube Webmail instances before version 1.5.13 and 1.6 before 1.6.13 are affected.
💻 Affected Systems
- Roundcube Webmail
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Attackers could perform UI redressing attacks, steal sensitive information through CSS-based data exfiltration, or conduct phishing attacks by manipulating the email interface.
Likely Case
Limited UI manipulation, potential for minor data leakage through CSS selectors, or disruption of email interface functionality.
If Mitigated
With proper input validation and output encoding, impact is limited to cosmetic UI changes with no data compromise.
🎯 Exploit Status
Exploitation requires the ability to inject CSS, typically through user-controllable input fields. The vulnerability is in comment handling within CSS parsing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Roundcube Webmail 1.5.13 and 1.6.13
Vendor Advisory: https://github.com/roundcube/roundcubemail/security/advisories
Restart Required: No
Instructions:
1. Backup your Roundcube installation and database. 2. Download the latest version from https://roundcube.net/download/. 3. Replace the existing installation files with the patched version. 4. Clear browser caches and test functionality.
🔧 Temporary Workarounds
Input Validation Filter
allImplement server-side input validation to sanitize CSS-related inputs before processing.
# Custom PHP filter to sanitize CSS input
function sanitizeCSS($input) {
return preg_replace('/[^a-zA-Z0-9\s\-_:.#(),%]/', '', $input);
}
🧯 If You Can't Patch
- Implement Content Security Policy (CSP) headers to restrict inline styles and external CSS sources.
- Deploy a web application firewall (WAF) with CSS injection detection rules.
🔍 How to Verify
Check if Vulnerable:
Check the Roundcube version in the config/version.inc.php file or via the web interface's About page.Check Version:
grep -r 'RCMAIL_VERSION' config/version.inc.phpVerify Fix Applied:
Verify the version is 1.5.13 or higher for 1.5.x branch, or 1.6.13 or higher for 1.6.x branch.📡 Detection & Monitoring
Log Indicators:
- Unusual CSS patterns in user input logs
- Multiple failed CSS parsing attempts in application logs
Network Indicators:
- Unusual CSS payloads in HTTP requests to Roundcube endpoints
SIEM Query:
source="roundcube_logs" AND (css OR style OR injection)🔗 References
- https://github.com/roundcube/roundcubemail/commit/1f4c3a5af5033747f9685a8a395dbd8228d19816
- https://github.com/roundcube/roundcubemail/commit/2b5625f1d2ef7e050fd1ae481b2a52dc35466447
- https://github.com/roundcube/roundcubemail/commit/53d75d5dfebef235a344d476b900c20c12d52b01
- https://github.com/roundcube/roundcubemail/commit/5a3315cce587e0be58335d11ff9a5571c90494a5
- https://github.com/roundcube/roundcubemail/commit/bf89cbaa5897d8ad62e8057d9a3f6babb90b7954
- https://github.com/roundcube/roundcubemail/commit/c15f5dbf093a497e19a749b20e7f8fb5a9c24cde
- https://github.com/roundcube/roundcubemail/releases/tag/1.5.13
- https://github.com/roundcube/roundcubemail/releases/tag/1.6.13
- https://roundcube.net/news/2026/02/08/security-updates-1.6.13-and-1.5.13
