CVE-2026-83627: Code Injection (CVSS 9.8)

Description

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.

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CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0082

Probability of exploitation

0.56%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-94 CWE-94

References

Other References

https://plugins.trac.wordpress.org/browser/hummingbird-performance/trunk/core/modules/class-page-cache.php#L1973 https://plugins.trac.wordpress.org/browser/hummingbird-performance/trunk/core/modules/class-page-cache.php#L1982 https://plugins.trac.wordpress.org/browser/hummingbird-performance/trunk/core/modules/class-page-cache.php#L749 https://plugins.trac.wordpress.org/browser/hummingbird-performance/trunk/core/modules/class-page-cache.php#L752 https://plugins.trac.wordpress.org/changeset/3675836/hummingbird-performance/trunk/core/modules/class-page-cache.php https://plugins.trac.wordpress.org/changeset?old_path=%2Fhummingbird-performance/tags/3.20.0&new_path=%2Fhummingbird-performance/tags/3.21.2 https://plugins.trac.wordpress.org/changeset?reponame=&new=3675836%40hummingbird-performance%2Ftags%2F3.21.2&old=3614991%40hummingbird-performance%2Ftags%2F3.20.0 https://www.wordfence.com/threat-intel/vulnerabilities/id/65c3ca36-79e6-47f8-9524-27e7631f4caf?source=cve

Frequently Asked Questions

What is CVE-2026-83627? +

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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-83627? +

CVE-2026-83627 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0082, placing it in the 1th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-83627? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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