CVE-2021-31404

What it is

Non-constant-time comparison of CSRF tokens in UIDL request handler in com.vaadin:flow-server versions 1.0.0 through 1.0.13 (Vaadin 10.0.0 through 10.0.16), 1.1.0 prior to 2.0.0 (Vaadin 11 prior to 14), 2.0.0 through 2.4.6 (Vaadin 14.0.0 through 14.4.6), 3.0.0 prior to 5.0.0 (Vaadin 15 prior to 18), and 5.0.0 through 5.0.2 (Vaadin 18.0.0 through 18.0.5) allows attacker to guess a security token via timing attack.

At a glance

Exploitability

Can be exploited locally on the machine without logging in. Limited direct impact.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-04-23 16:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:51 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 4.0 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-04-23 16:15 UTC

Last modified

2026-06-17 03:51 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-208

Record status

Modified

Affected

• Vaadin Flow < 1.0.14
• Vaadin Flow < 2.0.0
• Vaadin Flow < 2.4.7
• Vaadin Flow < 5.0.0
• Vaadin Flow < 5.0.3
• Vaadin < 10.0.17
• Vaadin < 14.0.0
• Vaadin < 14.4.7

Attack profile CVSS 3.1 · 4.0

Attack vector

Local

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-31404.md and follow it. Check whether this project is affected by CVE-2021-31404. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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