CVE-2021-24124Public exploitNetwork attack vector

Unauthenticated XSS via unencoded request URI

Published Mar 18, 2021 · Updated Aug 3, 2024

Cross-site scripting in WP Shieldon - WordPress Firewall 1.6.3 and earlier allows remote attackers to execute script through a CAPTCHA page. The CAPTCHA handler echoes the HTTP REQUEST_URI value into the response without output encoding, allowing a crafted URL to inject script into a viewer's browser. No authentication is required, but user interaction with the CAPTCHA page is required; the documented impact is script execution that can enable actions in the viewer's security context.

CVSS severity6.1
Medium
EPSS probability1.15%
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 WP Shieldon - WordPress Firewall 1.6.3 and earlier allows remote attackers to execute script through a CAPTCHA page. The CAPTCHA handler echoes the HTTP REQUEST_URI value into the response without output encoding, allowing a crafted URL to inject script into a viewer's browser. No authentication is required, but user interaction with the CAPTCHA page is required; the documented impact is script execution that can enable actions in the viewer's security context.

The record

CVE
CVE-2021-24124
Published
Mar 18, 2021
Updated
Aug 3, 2024
Vendor
Terry Lin
Product
WP Shieldon - WordPress Firewall
Classifications
CWE-79, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 18, 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=1.6.3 <=1.6.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Terry Lin · WP Shieldon - WordPress Firewallversion=1.6.3 <=1.6.3

Published CVSS scores

4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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')
T1189Drive-by Compromise

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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