CVE-2021-3824Network attack vector

Cross-site scripting via crafted login-page URL

Published Sep 23, 2021 · Updated Aug 3, 2024

Cross-site scripting in OpenVPN Access Server 2.9.0 through 2.9.4 allows remote attackers to inject script or HTML via the web login URL. The login page places attacker-controlled URL content into generated HTML without neutralizing encoded URI schemes. No authentication is required, but a user must open the crafted URL; the injected content can read or alter data available to the page.

CVSS severity6.1
Medium
EPSS probability0.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in OpenVPN Access Server 2.9.0 through 2.9.4 allows remote attackers to inject script or HTML via the web login URL. The login page places attacker-controlled URL content into generated HTML without neutralizing encoded URI schemes. No authentication is required, but a user must open the crafted URL; the injected content can read or alter data available to the page.

The record

CVE
CVE-2021-3824
Published
Sep 23, 2021
Updated
Aug 3, 2024
Vendor
OpenVPN Inc.
Product
OpenVPN Access Server
Classifications
CWE-79, CWE-84, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=2.9.0 through 2.9.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenVPN Inc. · OpenVPN Access Serverversion=2.9.0 through 2.9.4

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-84Improper Neutralization of Encoded URI Schemes in a Web Page
T1204.001User Execution: Malicious Link

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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