CVE-2021-31411

Browser code injection via writable temporary resources

Published May 5, 2021 · Updated Sep 16, 2024

Insecure temporary-file handling in Vaadin Flow Server 2.0.9 through 2.5.2 and 3.0 through 6.0.5 allows local users to inject browser code. Frontend preparation copies JAR resources through the operating system's shared default temporary directory, permitting another local process to watch for and modify them before incorporation into the application. Exploitation requires a build on a *NIX system and local low-privileged access; injected code executes in an end user's browser and can expose or alter browser-accessible data.

CVSS severity6.3
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insecure temporary-file handling in Vaadin Flow Server 2.0.9 through 2.5.2 and 3.0 through 6.0.5 allows local users to inject browser code. Frontend preparation copies JAR resources through the operating system's shared default temporary directory, permitting another local process to watch for and modify them before incorporation into the application. Exploitation requires a build on a *NIX system and local low-privileged access; injected code executes in an end user's browser and can expose or alter browser-accessible data.

The record

CVE
CVE-2021-31411
Published
May 5, 2021
Updated
Sep 16, 2024
Vendor
Vaadin
Product
Flow Server
Classifications
CWE-379, T1195.001
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.0.9 <* changes=[{"at":"3.0.0","status":"affected"},{"at":"6.0.0","status":"unaffected"},{"at":"6.0.0","status":"affected"}]

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Vaadin · Flow Serverversion=2.0.9 <* changes=[{"at":"3.0.0","status":"affected"},{"at":"6.0.0","status":"unaffected"},{"at":"6.0.0","status":"affected"}]
Vaadin · Vaadin Frameworkversion=14.0.3 <* changes=[{"at":"15.0.0","status":"affected"},{"at":"19.0.0","status":"unaffected"},{"at":"19.0.0","status":"affected"}]

Published CVSS scores

6.3VaadinCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-379Creation of Temporary File in Directory with Insecure Permissions
T1195.001Compromise Software Dependencies and Development Tools

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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