How severe is CVE-2021-31406?

CVE-2021-31406 has a CVSS 3.x base score of 4.0, rated medium severity. It is exploitable over local access with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-31406 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31406?

CVE-2021-31406 primarily affects Vaadin Flow. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31406?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-31406 published?

CVE-2021-31406 was published on 2021-04-23 and last updated on 2026-06-17.

CVE-2021-31406

CVE-2021-31406 is a medium-severity vulnerability in Vaadin Flow with a CVSS 3.x base score of 4.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-203.

Key facts

Severity: Medium (CVSS 3.x base score 4.0)
CVSS v2: 1.9
EPSS exploit prediction: 0% (11th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-203
Affected product: Vaadin Flow
Published: 2021-04-23
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-31406?: 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.
How severe is CVE-2021-31406?: CVE-2021-31406 has a CVSS 3.x base score of 4.0, rated medium severity. It is exploitable over local access with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-31406 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31406?: CVE-2021-31406 primarily affects Vaadin Flow. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31406?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-31406 published?: CVE-2021-31406 was published on 2021-04-23 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:a:vaadin:flow:*:*:*:*:*:*:*:*
cpe:2.3:a:vaadin:flow:6.0.0:-:*:*:*:*:*:*
cpe:2.3:a:vaadin:vaadin:*:*:*:*:*:*:*:*
cpe:2.3:a:vaadin:vaadin:19.0.0:-:*:*:*:*:*:*

More vulnerabilities in Vaadin Flow

CVE-2021-31407 — High (CVSS 8.6): Vulnerability in OSGi integration in com.vaadin:flow-server versions 1.2.0 through 2.4.7 (Vaadin 12.0.0 through…
CVE-2021-31405 — High (CVSS 7.5): Unsafe validation RegEx in EmailField component in com.vaadin:vaadin-text-field-flow versions 2.0.4 through 2.3.2…
CVE-2021-31411 — Medium (CVSS 6.3): Insecure temporary directory usage in frontend build functionality of com.vaadin:flow-server versions 2.0.9 through…
CVE-2021-31408 — Medium (CVSS 6.3): Authentication.logout() helper in com.vaadin:flow-client versions 5.0.0 prior to 6.0.0 (Vaadin 18), and 6.0.0 through…
CVE-2019-25027 — Medium (CVSS 6.1): Missing output sanitization in default RouteNotFoundError view in com.vaadin:flow-server versions 1.0.0 through 1.0.10…
CVE-2020-36321 — Medium (CVSS 5.9): Improper URL validation in development mode handler in com.vaadin:flow-server versions 2.0.0 through 2.4.1 (Vaadin…

All CVEs affecting Vaadin Flow →

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CVE-2024-25191 — Critical (CVSS 9.8): php-jwt 1.0.0 uses strcmp (which is not constant time) to verify authentication, which makes it easier to bypass…
CVE-2024-25190 — Critical (CVSS 9.8): l8w8jwt 2.2.1 uses memcmp (which is not constant time) to verify authentication, which makes it easier to bypass…

Browse all CWE-203 (Observable Discrepancy) vulnerabilities →