CVE-2021-33604

Reflected cross-site scripting in development mode handler in Vaadin 14, 15-19

2.5 LowFix available

URL encoding error in development mode handler in com.vaadin:flow-server versions 2.0.0 through 2.6.1 (Vaadin 14.0.0 through 14.6.1), 3.0.0 through 6.0.9 (Vaadin 15.0.0 through 19.0.8) allows local user to execute arbitrary JavaScript code by opening crafted URL in browser.

Attack profile

How easy it is to exploit

Attack vector: Local
Complexity: High
Privileges needed: None
User interaction: Required

What an attacker can affect

Confidentiality: Low
Integrity: None
Availability: None

Exploit likelihood

0.29%Down 0.1 points since Jun 25, 2021

What each source reports

CVE List Score used 2.5

Reflected cross-site scripting in development mode handler in Vaadin 14, 15-19

Record: CVE-2021-33604
CVSS 3.1: 2.5 LowCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
Weakness: CWE-172
Updated: 2026-11-02

EUVDEUVD-2021-1309 2.5

Record: EUVD-2021-1309
CVSS 3.1: 2.5 LowCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
Updated: 2026-11-03

GitHub AdvisoriesGHSA-c99r-67x4-whj6 2.5

Reflected cross-site scripting in development mode handler in Vaadin 14, 15-19

URL encoding error in development mode handler in com.vaadin:flow-server versions 2.0.0 through 2.6.1 (Vaadin 14.0.0 through 14.6.1), 3.0.0 through 6.0.9 (Vaadin 15.0.0 through 19.0.8) allows local user to execute arbitrary JavaScript code by opening crafted URL in browser.

https://vaadin.com/security/cve-2021-33604

Record: GHSA-c99r-67x4-whj6
CVSS 3.1: 2.5 LowCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
Weakness: CWE-172
Updated: 2026-11-02

NVD 2.5

Record: CVE-2021-33604
CVSS 3.1: 2.5 LowCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
CVSS 2.0: 1.2 LowAV:L/AC:H/Au:N/C:P/I:N/A:N
Weakness: CWE-172
Updated: 2026-11-02

OSV 2.5

Record: CVE-2021-33604
CVSS 3.1: 2.5 LowCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
Updated: 2026-11-06

OSVGHSA-c99r-67x4-whj6 2.5

Reflected cross-site scripting in development mode handler in Vaadin 14, 15-19

https://vaadin.com/security/cve-2021-33604

Record: GHSA-c99r-67x4-whj6
CVSS 3.1: 2.5 LowCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
Weakness: CWE-172
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`com.vaadin:vaadin-bom` Maven	14.0.0 to 14.6.1	14.6.2
`com.vaadin:vaadin-bom` Maven	15.0.0 to 19.0.8	19.0.9
`com.vaadin:vaadin-bom` Maven	14.0.0 up to 14.6.2, plus listed versions 14.0.114.0.1014.0.1114.0.1214.0.13 Show 45 moreShow less 14.0.1414.0.1514.0.214.0.314.0.414.0.514.0.614.0.714.0.814.0.914.1.014.1.114.1.1614.1.1714.1.1814.1.1914.1.214.1.2014.1.2114.1.2214.1.2314.1.2414.1.2514.1.2614.1.2714.1.2814.1.314.1.414.1.514.2.014.2.114.2.214.2.314.3.014.3.114.3.214.3.314.3.414.3.514.3.614.3.714.3.814.3.914.4.014.4.1	14.6.2
`com.vaadin:vaadin-bom` Maven	15.0.0 up to 19.0.9, plus listed versions 15.0.115.0.215.0.315.0.415.0.5 Show 35 moreShow less 15.0.616.0.016.0.116.0.216.0.316.0.416.0.517.0.017.0.117.0.1017.0.1117.0.217.0.317.0.417.0.617.0.717.0.817.0.918.0.018.0.118.0.218.0.318.0.418.0.518.0.618.0.719.0.019.0.119.0.219.0.319.0.419.0.519.0.619.0.719.0.8	19.0.9

History

History
Recorded	Changed	Sources
Nov 5, 2026	facts	OSV
Nov 3, 2026	aliases, products, published	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-33604 is a low vulnerability (CVSS 2.5) in Flow Flow-server, published June 24, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.29%, the 21st percentile. Fixed in com.vaadin:vaadin-bom 14.6.2.

References

This page doesn't list everything

Left out here: 17 versions. The JSON record has them.