CVE-2020-35217 is a high-severity (CVSS 8.8) Cross-Site Request Forgery (CSRF) vulnerability in io.vertx:vertx-web. A fix is available for io.vertx:vertx-web — see the affected versions and patch details below.
Cross-Site Request Forgery in Vert.x-Web framework
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-2020-35217 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 377,333 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
io.vertx:vertx-web☕io.vertx:vertx-web☕io.vertx:vertx-web☕io.vertx:vertx-webReal-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
Vert.x-Web framework v4.0 milestone 1-4 does not perform a correct CSRF verification. Instead of comparing the CSRF token in the request with the CSRF token in the cookie, it compares the CSRF token in the cookie against a CSRF token that is stored in the session. An attacker does not even need to provide a CSRF token in the request because the framework does not consider it. The cookies are automatically sent by the browser and the verification will always succeed, leading to a successful CSRF attack.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.vertx:vertx-web | ≥ 4.0.0-milestone1&&< 4.0.0-milestone5 | 4.0.0-milestone5io.vertx:vertx-web:4.0.0-milestone5 |
| ☕Maven | io.vertx:vertx-web | ≥ 4.0.0-milestone2&&< 4.0.0-milestone5 | 4.0.0-milestone5io.vertx:vertx-web:4.0.0-milestone5 |
| ☕Maven | io.vertx:vertx-web | ≥ 4.0.0-milestone3&&< 4.0.0-milestone5 | 4.0.0-milestone5io.vertx:vertx-web:4.0.0-milestone5 |
| ☕Maven | io.vertx:vertx-web | ≥ 4.0.0-milestone4&&< 4.0.0-milestone5 | 4.0.0-milestone5io.vertx:vertx-web:4.0.0-milestone5 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.vertx:vertx-web, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.vertx:vertx-web to 4.0.0-milestone5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-35217 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-2020-35217 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2020-35217. 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-2020-35217 in your dependencies?
O3 Security finds CVE-2020-35217 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.