WP Fastest Cache permits Host-header cache poisoning and stored XSS

WP Fastest Cache through 1.5.0 writes an untrusted HTTP Host value into cached script source URLs when Polylang or Polylang Pro is active and Combine JS is enabled. An unauthenticated attacker can poison the shared page cache so attacker-controlled JavaScript executes for subsequent visitors.

CVE / CNA score 7.2 CVSS 3.1 · security@wordfence.com

NVD score Pending NVD has not published its own CVSS assessment.

Component: WP Fastest Cache – WordPress Cache Plugin
Plugin slug: wp-fastest-cache
Affected: <= 1.5.0
Safe version: 1.5.1
Published: Aug 26, 2026
Weakness: CWE-79 — Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

This CVE was published Aug 26, 2026 and is one of 34 known issues for this plugin.

What to do

Update, patch or deactivate.

Update to 1.5.1 or later, purge all page and combined-JavaScript caches after updating, and invalidate privileged sessions if administrators visited poisoned pages.

A safe version is available, so updating to that version or later is the preferred remediation. If an immediate update is not practical, consider a targeted application patch or temporarily restricting the affected functionality.

Deactivate only when warranted by your risk profile, or when advised by your hosting provider in the limited circumstances where the vulnerability cannot otherwise be mitigated. If you’re unsure which action is appropriate, contact Fused or your hosting provider for guidance.

Source record

Technical description

The WP Fastest Cache – WordPress Cache Plugin plugin for WordPress is vulnerable to Stored Cross-Site Scripting via HTTP Host Header in all versions up to, and including, 1.5.0 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 Polylang or Polylang Pro plugin to be active and the Combine JS option to be enabled, as these conditions trigger the vulnerable Host-header-to-URL code path that writes attacker-controlled script src values into the shared page-cache file served to all subsequent visitors.

CVE / CNA vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

References

Primary and upstream sources

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