CVE-2026-74998: Roundcube Webmail

High severity, CVSS 7.2. EPSS: 0.4% chance of exploitation in the next 30 days.

In Roundcube Webmail before 1.6.18 and 1.7.x before 1.7.3, responses from the CSS (Cascading Style Sheets) proxy were not validated, which may result in information disclosure or XSS (cross-site scripting) via MIME sniffing.

Affected products

• Roundcube Webmail: from 1.6.0, before 1.6.18 (fixed in 1.6.18); from 1.7.0, before 1.7.3 (fixed in 1.7.3)

Published 2026-08-17. Last modified 2026-09-08.