Security readout for executives and security teams
Plain-English summary
A timing weakness in Vaadin’s Fusion endpoint CSRF token check could let an attacker infer token values by measuring response timing. The attack is difficult and low-impact compared with remote code execution, but exposed affected Vaadin applications should still upgrade because successful guessing could affect confidentiality and integrity.
Executive priority
Treat as a scheduled security maintenance item unless the affected application is highly sensitive or broadly reachable. No active exploitation is cited, but the flaw affects CSRF token protection and should not remain unpatched.
Technical view
CVE-2021-31406 is CWE-208 in Vaadin endpoint request handling. Non-constant-time CSRF token comparison affects com.vaadin:flow-server 3.0.0 through 5.0.3, corresponding to Vaadin 15.0.0 through 18.0.6, and com.vaadin:fusion-endpoint 6.0.0 in Vaadin 19.0.0.
Likely exposure
Exposure is likely limited to applications using affected Vaadin 15 through 19 Fusion endpoint components. The CVSS vector lists local attack vector and high attack complexity, so practical reach depends on how attackers can interact with the affected endpoint path.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. The vulnerability requires timing analysis against CSRF token comparison, which the CVSS score rates as high complexity with limited confidentiality and integrity impact.
Researcher notes
Focus review on Fusion endpoint request handling and dependency versions. Evidence supplied identifies the timing side channel and affected ranges, but does not provide exploit prevalence, operational indicators, or detailed remediation steps beyond vendor reference material.
Mitigation direction
- Check the Vaadin advisory for fixed versions and upgrade affected Vaadin components.
- Inventory Maven or Gradle dependencies for com.vaadin:flow-server and com.vaadin:fusion-endpoint.
- Prioritize applications exposing Fusion endpoints or handling sensitive workflows.
- Avoid treating network restrictions as a substitute for vendor remediation.
Validation and detection
- Confirm deployed Vaadin versions are outside the vulnerable ranges listed by Vaadin.
- Review dependency lockfiles and build output for affected component versions.
- Identify whether the application uses Vaadin Fusion endpoints.
- Run regression tests after upgrading Vaadin components.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-208: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCredential and access behavior lookup
The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-31406 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N1.42.5Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4MediumVector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://vaadin.com/security/cve-2021-31406CVE reference · x_refsource_MISC
- https://github.com/vaadin/flow/pull/10157CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Observable Timing Discrepancy
Observable Timing Discrepancy represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.