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CVE-2026-83627 – Unauthenticated Remote Code Execution – Hummingbird Performance WordPress Plugin (≤

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Summary

CVE-2026-83627 is a critical unauthenticated remote code execution vulnerability in the Hummingbird – Speed Optimization, Caching, Minify, Compress & CDN WordPress plugin (developed by WPMU DEV), affecting all versions up to and including 3.21.0. The flaw stems from a page-cache debug logging mechanism that writes unsanitized cookie data into a web-accessible PHP file, and carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: The log_msg() function in core/modules/class-page-cache.php writes debug log entries to wp-content/wphb-logs/page-caching-log.php, a file intended to be protected by a leading <?php die(); ?> header.
  • Trigger conditions: The protective header is written only if a class_exists( 'Filesystem' ) check passes; because class_exists() resolves the string in the global namespace while the actual class is HummingbirdCoreFilesystem, the check always fails, so the protective header is omitted when the log file is created or rotated during a front-end request.
  • Attack vector: The plugin’s cookie-handling routine writes the raw name of any cookie prefixed wphb_cache_ into the log file without sanitization, allowing an unauthenticated attacker to inject arbitrary PHP code via a crafted cookie name.
  • Impact: Because the file lacks the die() guard and contains attacker-controlled PHP, requesting the log file directly results in arbitrary PHP code execution on the server — full compromise of confidentiality, integrity, and availability.
  • Prerequisite: Page Caching with the Debug Log option must be enabled (non-default configuration) for the vulnerable log file to be generated.

Affected software

  • Hummingbird Performance – Cache & Page Speed Optimization for Core Web Vitals (wpmudev), all versions up to and including 3.21.0.

Severity

CVSS v3.1 Base Score: 9.8 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Update the Hummingbird plugin to version 3.21.2 or later, which addresses this issue.
  • If unable to patch immediately: Disable the Page Caching Debug Log option in the plugin settings, and remove/restrict web access to wp-content/wphb-logs/page-caching-log.php via server configuration until the update can be applied.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Raw response body: /wp-content/plugins/wp-hummingbird/

References

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1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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