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9.8

Hummingbird plugin lets attackers run code via cache log

CVE-2026-83627 · published today
Summary

The Hummingbird speed‑optimization plugin for WordPress can create a cache‑debug file that is publicly reachable and may miss its safety header. An attacker can place malicious code in that file simply by sending a crafted cookie, then trigger the file to run and take control of the site. Turn off the page‑caching debug log or update the plugin to a version that fixes the file‑creation logic.

What to do

The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.

Affected software
VendorProductAffected versions
wpmudev hummingbird performance – cache & page speed optimization for core web vitals | critical css | minify css | defer css javascript | cdn <= 3.21.0
Original advisory text
The Hummingbird – Speed Optimization, Caching, Minify, Compress & CDN plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 3.21.0 via the log_msg() func...
The Hummingbird – Speed Optimization, Caching, Minify, Compress & CDN plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 3.21.0 via the log_msg() function in core/modules/class-page-cache.php. The page-cache debug log is written to wp-content/wphb-logs/page-caching-log.php, a directly web-accessible PHP file that is supposed to be protected by a leading '<?php die(); ?>' header. That header is guarded by class_exists( 'Filesystem' ), which can never match because class_exists() resolves string arguments in the global namespace while the class is Hummingbird\Core\Filesystem; when the log is created during a front-end request the header is therefore omitted entirely. get_cookies() then writes the raw name of any cookie matching the wphb_cache_ prefix into that file without sanitization. This makes it possible for unauthenticated attackers to write arbitrary PHP into the log file with a single anonymous request and execute it by requesting the file directly, resulting in full remote code execution. Exploitation requires the site administrator to have enabled Page Caching with the Debug Log option (non-default), and the log file to be created during a front-end request — a state reached by the plugin's own 'Clear logs' action, any cache flush, or unattended via the plugin's daily log-rotation cron, which can strip the protective header from an existing log file.
References
Severity
9.8 Critical
CVSS 3.1: 9.8 (MITRE)
Type
CWE-94Code Injection
Timeline
Published5 Sep 2026
Updated5 Sep 2026
First seen5 Sep 2026
Sources
CVE-2026-83627 · NVD
CVE-2026-83627 · MITRE
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