WordPress security changelog
MEDIUM CVE-2026-76579 Deferred

LiteSpeed ESI validation and execution use different request values

An unauthenticated attacker must supply a validly signed esi query value while placing a separate malicious esi value in the POST body. With PHP's default request-merge order, the POST value wins at execution even though the query value was validated. Reflected script execution also requires victim interaction. The export does not explain how the attacker obtains the valid signed value; it does not establish signature forgery. Authoritative affected range: <= 7.9. Confirmed remediation: 7.9.1.

CVE / CNA score 4.7 CVSS 3.1 · security@wordfence.com
NVD score Pending NVD has not published its own CVSS assessment.
Component
LiteSpeed Cache
Plugin slug
litespeed-cache
Affected
<= 7.9
Safe version
7.9.1
Published
Sep 19, 2026
Weakness
CWE-79 — Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

This CVE was published Sep 19, 2026 and is one of 23 known issues for this plugin.

What to do

Update, patch or deactivate.

Confirmed fixed release: 7.9.1. The release binds ESI execution to the signed query payload so POST values cannot replace validated data. Official changelog: https://wordpress.org/plugins/litespeed-cache/#developers . Bind execution to the exact verified query payload and reject ambiguous duplicate parameters across request sources. Avoid untrusted ESI links or form submissions until updated.

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 LiteSpeed Cache plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the 'esi' parameter in all versions up to, and including, 7.9 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link. Exploitation requires that the attacker supply a validly signed 'esi' value in the GET query string while submitting a separate attacker-controlled 'esi' payload as a POST body field, relying on PHP's default $_REQUEST merge order to have the POST value take precedence at the point of execution.

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

References

Primary and upstream sources