XSS in Boldgrid W3 Total Cache

CVE-2026-78438

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.

Vulnerability class: XSS (Cross-Site Scripting)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.005 (41.4th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 41.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-78438: held from 0.003 to 0.005.

EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-78438?
CVE-2026-78438 is a high-severity vulnerability in Boldgrid W3 Total Cache, classified under Cross-site Scripting. CVSS score: 7.2/10. Published 2026-09-05.
How severe is CVE-2026-78438?
High severity. CVSS v3 base score is 7.2 out of 10.