CVE-2021-24241Public exploitNetwork attack vector

Administrator-session script execution via unescaped update URL

Published Apr 22, 2021 · Updated Aug 3, 2024

Reflected XSS in Advanced Custom Fields PRO before 5.9.1 allows remote attackers to execute script in an administrator's browser. The update settings page places its generated update URL into an HTML attribute without escaping, so a crafted query suffix terminates the attribute and injects script. An authenticated administrator must open the crafted URL; the script then runs in that WordPress session and can read session-accessible data or issue same-origin requests.

CVSS severity6.1
Medium
EPSS probability1.39%
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 Advanced Custom Fields PRO before 5.9.1 allows remote attackers to execute script in an administrator's browser. The update settings page places its generated update URL into an HTML attribute without escaping, so a crafted query suffix terminates the attribute and injects script. An authenticated administrator must open the crafted URL; the script then runs in that WordPress session and can read session-accessible data or issue same-origin requests.

The record

CVE
CVE-2021-24241
Published
Apr 22, 2021
Updated
Aug 3, 2024
Vendor
WP Engine
Product
Advanced Custom Fields PRO
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 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=5.9.1 <5.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

WP Engine · Advanced Custom Fields PROversion=5.9.1 <5.9.1

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NIST NVDCVSS: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 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')
T1204.001User Execution: Malicious Link

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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