Security readout for executives and security teams
Plain-English summary
CVE-2021-31404 is a timing side-channel issue in Vaadin's UIDL request handler. A non-constant-time CSRF token comparison could let an attacker infer a security token by measuring response timing. The published severity is medium with CVSS 4.0, and the bundle does not show known active exploitation.
Executive priority
Treat this as a moderate remediation item. It affects authentication-related token handling, but exploitation appears difficult and no active exploitation is cited. Patch during the next normal security maintenance window unless the affected app is highly sensitive or exposed.
Technical view
Affected com.vaadin:flow-server versions compare CSRF tokens in non-constant time, creating CWE-208 exposure. The impacted ranges cover Vaadin 10, 11 through pre-14, 14.0.0 through 14.4.6, 15 through pre-18, and 18.0.0 through 18.0.5. Successful exploitation requires a high-complexity timing attack.
Likely exposure
Exposure is limited to applications using affected Vaadin or flow-server versions listed in the advisory. Systems not using Vaadin Flow, or running versions outside the affected ranges, are not indicated as affected by the provided sources.
Exploitation context
The source bundle says attackers may guess a security token through timing analysis. It does not cite public exploit code, real-world exploitation, or CISA KEV listing. The CVSS vector indicates high attack complexity and no required privileges or user interaction.
Researcher notes
Focus validation on Vaadin Flow server versions and UIDL request handling. The useful evidence is version-based rather than exploit-based. Avoid assuming exploitability without timing conditions, reachable UIDL handling, and an affected dependency version.
Mitigation direction
- Inventory applications using Vaadin Flow or com.vaadin:flow-server.
- Upgrade to a vendor-supported version outside the affected ranges.
- Prioritize internet-exposed or sensitive Vaadin applications first.
- Check Vaadin's advisory for branch-specific fixed versions.
- Retest affected applications after dependency updates.
Validation and detection
- Review dependency manifests for com.vaadin:flow-server versions.
- Map Vaadin framework versions against the affected ranges.
- Confirm the deployed artifact uses the updated dependency tree.
- Check scanner findings against Vaadin's CVE advisory.
- Document any accepted risk for unsupported Vaadin branches.
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-2021-31404 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-2021-31404CVE reference · x_refsource_MISC
- https://github.com/vaadin/flow/pull/9875CVE 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.