CVE-2021-33604 | 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.

Published: 2021-06-24 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-33604 is rated Low Risk (15.6/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.05%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-33604

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2023-03-07 0.89% 0.05% -0.83%
2 2022-04-01 1.40% 0.89% -0.52%
3 2022-02-04 — 1.40% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-33604

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
2.5 3.1 LOW
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.0 1.4 [email protected]
2.5 3.1 LOW
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.0 1.4 [email protected]
1.2 2.0 LOW
AV:L/AC:H/Au:N/C:P/I:N/A:N Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:H)
Exploitation requires uncommon or highly specific conditions.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 1.9 2.9 [email protected]

Weakness enumeration for CVE-2021-33604

GitHub Security Advisory for CVE-2021-33604

GHSA-c99r-67x4-whj6 · Severity: low · Ecosystem: maven — Reflected cross-site scripting in development mode handler in Vaadin 14, 15-19

Affected software / configurations for CVE-2021-33604

Vendor Product Version Raw CPE
vaadin flow-server >= 2.0.0, <= 2.6.1 cpe:2.3:a:vaadin:flow-server:*:*:*:*:*:*:*:*
vaadin flow-server >= 3.0.0, <= 5.0.0 cpe:2.3:a:vaadin:flow-server:*:*:*:*:*:*:*:*
vaadin flow-server >= 6.0.0, <= 6.0.9 cpe:2.3:a:vaadin:flow-server:*:*:*:*:*:*:*:*
vaadin vaadin >= 14.0.0, <= 14.6.1 cpe:2.3:a:vaadin:vaadin:*:*:*:*:*:*:*:*
vaadin vaadin >= 15.0.0, <= 18.0.0 cpe:2.3:a:vaadin:vaadin:*:*:*:*:*:*:*:*
vaadin vaadin >= 19.0.0, <= 19.0.8 cpe:2.3:a:vaadin:vaadin:*:*:*:*:*:*:*:*

References for CVE-2021-33604

cvelogic Threat Intelligence