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HIGH severity

CVE-2020-36321 — flow-server

HIGHFix: vaadin/flow#9392

CVE-2020-36321 is a high-severity (CVSS 7.5) Path Traversal vulnerability in com.vaadin:flow-server. A fix is available for com.vaadin:flow-server — see the affected versions and patch details below.

Directory traversal in development mode handler in Vaadin 14 and 15-17

Also known asGHSA-49r2-73m6-pp8f
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2020-36321 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected
☕com.vaadin:flow-server☕com.vaadin:flow-server

Real-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

Improper URL validation in development mode handler in com.vaadin:flow-server versions 2.0.0 through 2.4.1 (Vaadin 14.0.0 through 14.4.2), and 3.0 prior to 5.0 (Vaadin 15 prior to 18) allows attacker to request arbitrary files stored outside of intended frontend resources folder.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavencom.vaadin:flow-server≥ 3.0.0&&< 5.0.05.0.0com.vaadin:flow-server:5.0.0
☕Mavencom.vaadin:flow-server≥ 2.0.0&&< 2.4.22.4.2com.vaadin:flow-server:2.4.2

Affected Products

2 products · 4 configurations
Application
flowvaadin
≥ 3.0.0 && < 5.0.0
range
Application
vaadinvaadin
≥ 15.0.0 && < 18.0.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.vaadin:flow-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update com.vaadin:flow-server to 5.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-36321 is resolved across your whole dependency graph.

  3. Workarounds

    Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

Improper URL validation in development mode handler in `com.vaadin:flow-server` versions 2.0.0 through 2.4.1 (Vaadin 14.0.0 through 14.4.2), and 3.0 prior to 5.0 (Vaadin 15 prior to 18) allows attacker to request arbitrary files stored outside of intended frontend resources folder. - https://vaadin.com/security/cve-2020-36321
O3 Security · Impact-Aware SCA

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CVE-2020-36321: flow-server — Fixed in 5.0.0