CVE-2021-24503Public exploitNetwork attack vector

Stored XSS via unsanitized shortcode attributes

Published Aug 2, 2021 · Updated Aug 3, 2024

Stored XSS in Theme Mason Popular Brand Icons – Simple Icons before 2.7.8 allows remote authenticated users to execute script via shortcodes. The simple_icon shortcode emits the color, size, and class attributes into frontend SVG markup without sanitizing or validating them. Contributor posts require administrator approval before the payload runs, while editors can publish it directly even without unfiltered_html.

CVSS severity5.4
Medium
EPSS probability0.62%
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 Theme Mason Popular Brand Icons – Simple Icons before 2.7.8 allows remote authenticated users to execute script via shortcodes. The simple_icon shortcode emits the color, size, and class attributes into frontend SVG markup without sanitizing or validating them. Contributor posts require administrator approval before the payload runs, while editors can publish it directly even without unfiltered_html.

The record

CVE
CVE-2021-24503
Published
Aug 2, 2021
Updated
Aug 3, 2024
Vendor
Theme Mason
Product
Popular Brand Icons – Simple Icons
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 2, 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=2.7.8 <2.7.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Theme Mason · Popular Brand Icons – Simple Iconsversion=2.7.8 <2.7.8

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')
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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