CVE-2021-24153Public exploitNetwork attack vector

Authenticated stored XSS via blacklist filter bypass

Published Apr 5, 2021 · Updated Aug 3, 2024

Stored XSS in Yoast SEO before 3.4.1 allows remote authenticated users to store script content that executes in another user's browser. The published advisory does not identify the affected field or handler; it states that crafted input bypasses a blacklist for parentheses and functions such as alert. Exploitation requires authenticated access and subsequent rendering by another user, enabling script execution in that user's browser context.

CVSS severity5.4
Medium
EPSS probability1.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Yoast SEO before 3.4.1 allows remote authenticated users to store script content that executes in another user's browser. The published advisory does not identify the affected field or handler; it states that crafted input bypasses a blacklist for parentheses and functions such as alert. Exploitation requires authenticated access and subsequent rendering by another user, enabling script execution in that user's browser context.

The record

CVE
CVE-2021-24153
Published
Apr 5, 2021
Updated
Aug 3, 2024
Vendor
Yoast
Product
Yoast SEO
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 5, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=3.4.1 <3.4.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Yoast · Yoast SEOversion=3.4.1 <3.4.1

Published CVSS scores

3.5NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NVDCVSS:3.1/AV:N/AC:L/PR:L/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

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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