CVE-2021-31403 is a low-severity (CVSS 2.5) CWE-208 vulnerability in com.vaadin:vaadin-bom. A fix is available for com.vaadin:vaadin-bom — see the affected versions and patch details below.
Timing side channel vulnerability in UIDL request handler in Vaadin 7 and 8
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-31403 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
com.vaadin:vaadin-bom☕com.vaadin:vaadin-bom☕com.vaadin:vaadin-server☕com.vaadin:vaadin-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Non-constant-time comparison of CSRF tokens in UIDL request handler in com.vaadin:vaadin-server versions 7.0.0 through 7.7.23 (Vaadin 7.0.0 through 7.7.23), and 8.0.0 through 8.12.2 (Vaadin 8.0.0 through 8.12.2) allows attacker to guess a security token via timing attack
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | com.vaadin:vaadin-bom | ≥ 7.0.0&&< 7.7.24 | 7.7.24com.vaadin:vaadin-bom:7.7.24 |
| ☕Maven | com.vaadin:vaadin-bom | ≥ 8.0.0&&< 8.12.3 | 8.12.3com.vaadin:vaadin-bom:8.12.3 |
| ☕Maven | com.vaadin:vaadin-server | ≥ 7.0.0&&< 7.7.24 | 7.7.24com.vaadin:vaadin-server:7.7.24 |
| ☕Maven | com.vaadin:vaadin-server | ≥ 8.0.0&&< 8.12.3 | 8.12.3com.vaadin:vaadin-server:8.12.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.vaadin:vaadin-bom, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update com.vaadin:vaadin-bom to 7.7.24 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-31403 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-31403 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-31403. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-31403 in your dependencies?
O3 Security finds CVE-2021-31403 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.