CVE-2021-31406: Vaadin Flow

Low severity, CVSS 2.5. EPSS: 0.2% chance of exploitation in the next 30 days.

Non-constant-time comparison of CSRF tokens in endpoint request handler in com.vaadin:flow-server versions 3.0.0 through 5.0.3 (Vaadin 15.0.0 through 18.0.6), and com.vaadin:fusion-endpoint version 6.0.0 (Vaadin 19.0.0) allows attacker to guess a security token for Fusion endpoints via timing attack.

Affected products

• Vaadin Flow: from 3.0.0, before 5.0.4 (fixed in 5.0.4); version 6.0.0 only
• Vaadin Vaadin: from 15.0.0, before 18.0.7 (fixed in 18.0.7); version 19.0.0 only

Published 2021-04-23. Last modified 2026-06-17.