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NVD / CVE Program· CNA Vaadin

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

Noroxi assessment

Priority: Monitor (action score 10/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.21% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: com.vaadin:flow-server (Maven) 5.0.4, 6.0.1.

Low priority for now. Upgrade to com.vaadin:flow-server (Maven) 5.0.4, 6.0.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

LowCVSS 2.5 · v3.1—No exploit Fix available
Published
Apr 23, 2021
Updated
Jun 16, 2026
EPSS
0.2% · 11th percentile

Report tools

JSON

Action score

10

Monitor

Low priority for now.

CVSS
10 / 40 · 2.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CNA vs NVD score

NVD
2.5
CNA · Vaadin
4.0
1.5 point gap

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
vaadinflow
vaadinvaadin

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • vaadin flow3.0.0 and later · before 5.0.4
  • vaadin flow6.0.0
  • vaadin vaadin15.0.0 and later · before 18.0.7
  • vaadin vaadin19.0.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Vaadin). Independent of NVD's CPE analysis and usually ahead of it.

  • Vaadin flow-server

    • 6.0.0affected
    • 3.0.0 and lateraffected

  • Vaadin Vaadin

    • 19.0.0affected
    • 15.0.0 and lateraffected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Mavencom.vaadin:flow-serverfrom 3.0.0 · before 5.0.45.0.4
Mavencom.vaadin:flow-serverfrom 6.0.0 · before 6.0.16.0.1

Same product

vaadin: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-31411Insecure temporary directory usage in frontend build functionality of Vaadin 14 and 15-19
    31Monitor
  • CVE-2021-31407Server classes and resources exposure in OSGi applications using Vaadin 12-14 and 19
    31Monitor
  • CVE-2021-31405Regular expression denial of service (ReDoS) in EmailField component in Vaadin 14 and 15-17
    30Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2020-36321Apr 23, 2021 · Directory traversal in development mode handler in Vaadin 14 and 15-17
    30Monitor
  • ← EarlierCVE-2021-31404Apr 23, 2021 · Timing side channel vulnerability in UIDL request handler in Vaadin 10, 11-14, and 15-18
    10Monitor
  • Later →CVE-2021-31408Apr 23, 2021 · Server session is not invalidated when logout() helper method of Authentication module is used in Vaadin 18-19
    28Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Maven:com.vaadin:flow-server5.0.4Package registry (OSV)
Maven:com.vaadin:flow-server6.0.1Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
low · data can be read
Integrity
none
Availability
none
Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
None
Availability impact
None

Weakness class (CWE)

CWE-208 · Observable Timing Discrepancy

CVSS vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records