What’s Vulnerable › Vulnerabilities

CVE-2021-31406: Timing side channel vulnerability in endpoint request handler in Vaadin 15-19

• Severity: low (CVSS 2.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-04-23 · updated 2026-06-17
• Weakness: CWE-208

Description

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; 6.0.0 — fixed in 5.0.4
• Vaadin: from 15.0.0 before 18.0.7; 19.0.0 — fixed in 18.0.7

How to fix

Upgrade to a fixed version: vaadin flow 5.0.4; Vaadin 18.0.7. Check the vendor advisory for mitigations.

References

• https://github.com/vaadin/flow/pull/10157
• https://vaadin.com/security/cve-2021-31406
• https://github.com/vaadin/flow/pull/10157
• https://vaadin.com/security/cve-2021-31406

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