CVE-2021-31406
Timing side channel vulnerability in endpoint request handler in Vaadin 15-19
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.
Attack profile
How easy it is to exploit
- Attack vector
- Local
- Complexity
- High
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
Timing side channel vulnerability in endpoint request handler in Vaadin 15-19
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.
- Record
CVE-2021-31406- CVSS 3.1
- 4.0 Medium
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-208
- Updated
- 2026-11-02
EUVDEUVD-2021-0850
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.
- Record
EUVD-2021-0850- CVSS 3.1
- 4.0 Medium
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-p7jq-v8jp-j424
Timing side channel vulnerability in endpoint request handler in Vaadin 15-19
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.
- Record
GHSA-p7jq-v8jp-j424- CVSS 3.1
- 4.0 Medium
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-203, CWE-208
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2021-31406- CVSS 3.1
- 4.0 Medium
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N - CVSS 3.1
- 2.5 Low
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N - CVSS 2.0
- 1.9 Low
AV:L/AC:M/Au:N/C:P/I:N/A:N - Weakness
- CWE-208, CWE-203
- Updated
- 2026-11-02
OSV
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.
- Record
CVE-2021-31406- CVSS 3.1
- 2.5 Low
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N - Updated
- 2026-11-02
OSVGHSA-p7jq-v8jp-j424
Timing side channel vulnerability in endpoint request handler in Vaadin 15-19
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.
- Record
GHSA-p7jq-v8jp-j424- CVSS 3.1
- 4.0 Medium
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-203, CWE-208
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
com.vaadin:flow-serverMaven |
3.0.0 up to 5.0.4 | 5.0.4 |
com.vaadin:flow-serverMaven |
6.0.0 to 6.0.0 | 6.0.1 |
com.vaadin:flow-serverMaven |
3.0.0 up to 5.0.4, plus listed versions 3.0.13.0.23.0.33.0.43.0.5 Show 22 moreShow less3.0.63.0.73.1.03.1.13.1.23.1.33.1.53.1.63.1.74.0.04.0.14.0.24.0.34.0.44.0.54.0.64.0.74.0.85.0.05.0.15.0.25.0.3 |
5.0.4 |
com.vaadin:flow-serverMaven |
6.0.0 up to 6.0.1 | 6.0.1 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases, products | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-31406 is a medium vulnerability (CVSS 4.0) in Flow Flow-server, published April 19, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.21%, the 11th percentile. Fixed in com.vaadin:flow-server 5.0.4.