WordPress security changelog
HIGH CVE-2026-3375 Deferred

LiteSpeed Cache CSS callbacks can store script behind bypassable IP validation

An unauthenticated attacker who can bypass the IP-based QUIC.cloud callback validation under certain reverse-proxy, load-balancer or CDN configurations can submit CSS content to /wp-json/litespeed/v1/notify_ccss or /wp-json/litespeed/v1/notify_ucss. The endpoints save the content to disk without sanitization, and later frontend loads render it inline without output escaping. Injected JavaScript executes in the site's origin when that output is viewed. The exact bypass configuration is unspecified; ordinary unauthenticated access is not enough by itself. Affected versions: <= 7.7. Confirmed fixed release: 7.8, based on the official change filtering HTML tags when saving CSS content.

CVE / CNA score 7.2 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
<= 7.7
Safe version
7.8
Published
May 27, 2026
Weakness
CWE-79 — Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

This CVE was published May 27, 2026 and is one of 23 known issues for this plugin.

What to do

Update, patch or deactivate.

Update LiteSpeed Cache to 7.8 or later, preferably the current supported release. Filter HTML markup out of callback-supplied CSS before storage and prevent generated inline CSS from escaping its output context. Authenticate each callback rather than relying only on a proxy-sensitive source-IP check; the current changelog also describes signature-based callback authorization. Review generated critical and unique CSS for injected markup and regenerate affected files after updating. Official changelog: https://wordpress.org/plugins/litespeed-cache/#developers

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 Stored Cross-Site Scripting via the /wp-json/litespeed/v1/notify_ccss and /wp-json/litespeed/v1/notify_ucss REST API endpoints in all versions up to, and including, 7.7. These endpoints accept CSS content from QUIC.cloud callback notifications and store it to disk without sanitization. The stored content is later rendered inline frontend page loads without output escaping. The access control protecting these endpoints is IP-based validation that can potentially be bypassed when the WordPress site is deployed behind a reverse proxy, load balancer, or CDN with certain configurations. This makes it possible for unauthenticated attackers, under certain conditions, to inject arbitrary JavaScript into CCSS/UCSS content.

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