CVE-2021-41836Network attack vector

Stored XSS via unescaped site ID

Published Dec 14, 2021 · Updated Feb 10, 2025

Stored XSS in the Fathom Analytics WordPress plugin 3.0.4 and earlier allows remote authenticated users to inject scripts via its site ID setting. The settings path stores the fathom_site_id value and renders it from fathom-analytics.php without sufficient input validation or output escaping. Administrator access is required, and execution requires unfiltered_html to be disabled, including on affected multisite installations, after a user opens the injected page.

CVSS severity4.8
Medium
EPSS probability0.56%
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 the Fathom Analytics WordPress plugin 3.0.4 and earlier allows remote authenticated users to inject scripts via its site ID setting. The settings path stores the fathom_site_id value and renders it from fathom-analytics.php without sufficient input validation or output escaping. Administrator access is required, and execution requires unfiltered_html to be disabled, including on affected multisite installations, after a user opens the injected page.

The record

CVE
CVE-2021-41836
Published
Dec 14, 2021
Updated
Feb 10, 2025
Vendor
Fathom Analytics
Product
Fathom Analytics
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Dec 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 10, 2025Record 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=3.0.4 <=3.0.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Fathom Analytics · Fathom Analyticsversion=3.0.4 <=3.0.4

Published CVSS scores

3.5NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
4.8WordfenceCVSS:3.1/AV:N/AC:L/PR:H/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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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

Public exploit references

No public exploit references are available in this record.

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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