CVE-2026-121763

Hummingbird Performance – Cache & Page Speed Optimization for Core Web Vitals | Critical CSS | Minify CSS | Defer CSS Javascript | CDN <= 3.21.2 - Authenticated (Subscriber+) Stored Cross-Site Scripting

2026-11-07 00:00
mroccon

Strategic Overview

Status
Patched in 4.0.0
Affected Plugin
Hummingbird Performance – Cache & Page Speed Optimization for Core Web Vitals | Critical CSS | Minify CSS | Defer CSS Javascript | CDN
Affected Version
<= 3.21.2
CVSS
6.4Medium
Weakness type
CWE-79 · Improper Neutralization of Input During Web Page Generation
CVE
CVE-2026-121763
View all Hummingbird Performance – Cache & Page Speed Optimization for Core Web Vitals | Critical CSS | Minify CSS | Defer CSS Javascript | CDN vulnerabilities

At a glance

CVE-2026-121763 is a medium-severity Improper Neutralization of Input During Web Page Generation vulnerability in the Hummingbird Performance WordPress plugin, affecting versions <= 3.21.2. It carries a CVSS score of 6.4 (reachable over the network; low attack complexity). Exploitation requires an authenticated account at Subscriber level or above. The issue is fixed in version 4.0.0; sites on affected versions should update now. Disclosed November 2026, reported by mroccon.

Vulnerability Overview

The Hummingbird Performance – Cache & Page Speed Optimization for Core Web Vitals | Critical CSS | Minify CSS | Defer CSS Javascript | CDN plugin for WordPress is vulnerable to Stored Cross-Site Scripting in all versions up to, and including, 3.21.2. This is due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with subscriber-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user.

CWE-79: Improper Neutralization of Input During Web Page Generation

Reaching this weakness in Hummingbird Performance <= 3.21.2 takes an account at Subscriber level or above. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.

Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For Hummingbird Performance the fix is 4.0.0: builds <= 3.21.2 are affected, anything from 4.0.0 onward is not.

Remediation

Update to version 4.0.0, or a newer patched version

How does WordSec protect against this?

An attacker needs Subscriber access first, so the firewall sees the attempt as traffic from a logged-in account: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Hummingbird Performance 4.0.0 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2026-121763https://www.wordfence.com/threat-intel/vulnerabilities/id/c1e7b324-fb3b-4816-82a4-7b9807a99e96https://nvd.nist.gov/vuln/detail/CVE-2026-121763

Related records

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