CVE-2021-21799Public exploitNetwork attack vector

Browser script execution via unescaped hostname

Published Jul 16, 2021 · Updated Aug 3, 2024

Reflected XSS in Advantech R-SeeNet 2.4.12 allows remote attackers to execute JavaScript in a targeted user's browser via a crafted URL. The telnet_form.php script reads the hostname HTTP query parameter and echoes it unescaped into the page's title element. Exploitation requires the targeted user to visit the crafted URL, but the user does not need to be logged in; script execution occurs in that browser context.

CVSS severity9.6
Critical
EPSS probability12.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in Advantech R-SeeNet 2.4.12 allows remote attackers to execute JavaScript in a targeted user's browser via a crafted URL. The telnet_form.php script reads the hostname HTTP query parameter and echoes it unescaped into the page's title element. Exploitation requires the targeted user to visit the crafted URL, but the user does not need to be logged in; script execution occurs in that browser context.

The record

CVE
CVE-2021-21799
Published
Jul 16, 2021
Updated
Aug 3, 2024
Vendor
Advantech
Product
R-SeeNet
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 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=Advantech R-SeeNet 2.4.12 (20.10.2020)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Advantech · R-SeeNetversion=Advantech R-SeeNet 2.4.12 (20.10.2020)

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
9.6Cisco TalosCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
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 exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

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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