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CVE-2026-58480 – Unauthenticated Arbitrary File Upload Leading to RCE – Blocksy Companion Pro (Wo…

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Summary

CVE-2026-58480 is a critical unauthenticated arbitrary file upload vulnerability in the Blocksy Companion Pro plugin for WordPress, developed by Creative Themes, affecting all versions before 2.1.47. By exploiting a flawed file extension validation routine in the plugin’s Custom Fonts extension, an unauthenticated attacker can upload a PHP webshell to the server and achieve full remote code execution (RCE). The vulnerability carries a CVSS v3.1 score of 9.8 (Critical).

Technical details

  • Root cause: The save_attachments function, exposed through the plugin’s Advanced Reviews feature, performs file extension validation using PHP’s strpos() function — a substring check rather than a strict suffix match. This logic can be bypassed by crafting a double-extension filename such as shell.woff2.php, where the whitelisted font extension (.woff2) appears as a substring of the full filename. The validation passes on the substring match, but the web server executes the uploaded file as PHP.
  • Trigger conditions: No authentication is required. The Advanced Reviews feature and Custom Fonts extension must be active on the target site; no user interaction or account credential is needed from the attacker’s side.
  • Attack vector: Network-accessible; the vulnerable file upload endpoint is reachable over HTTP/HTTPS without any credentials.
  • Impact: Successful exploitation allows an attacker to upload and execute arbitrary PHP code on the web server, resulting in full server compromise, data exfiltration, and potential lateral movement within the host environment.

Affected software

  • Blocksy Companion Pro (WordPress Plugin) — all versions before 2.1.47

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector String: 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 Blocksy Companion Pro plugin to version 2.1.47 or later. The patched release was made available on June 24, 2026, and version 2.1.48 is the current release as of this advisory. Updates can be applied through the WordPress admin dashboard or the Creative Themes account portal.
  • If immediate patching is not feasible, disable the Advanced Reviews feature and the Custom Fonts extension within the Blocksy Companion Pro settings as a temporary measure to reduce attack surface.
  • Audit web server upload directories for suspicious double-extension filenames (e.g., *.woff2.php, *.ttf.php) as potential indicators of prior compromise.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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