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CVE-2026-54194 – PHP Object Injection Leading to RCE – Avada Fusion Builder WordPress Plugin ≤ 3….

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Summary

CVE-2026-54194 is a critical PHP Object Injection vulnerability in the Fusion Builder WordPress plugin by ThemeFusion, affecting all versions up to and including 3.15.4. Assigned a CVSS score of 9.8 (Critical) with no privileges and no user interaction required per the official CVSS vector, this flaw can enable remote attackers to achieve arbitrary code execution if a suitable POP (Property-Oriented Programming) chain is present in the application’s codebase or co-installed plugins. ThemeFusion has released a patched version (3.15.5) and immediate upgrade is strongly recommended.

Technical details

  • Root cause: Improper deserialization of untrusted data (CWE-502) within the Fusion Builder plugin; attacker-controlled input is deserialized without adequate validation, enabling PHP object injection.
  • Trigger conditions: Exploitable remotely over the network with no user interaction required. The official CVSS vector assigns PR:N (no privileges required). Note that the CVE record title references "Contributor," which in WordPress naming conventions typically implies a Contributor-level account at minimum; this discrepancy between the title label and the CVSS PR:N metric has not been publicly resolved by the vendor or an independent researcher at time of publication, and the authoritative CVSS vector is used here.
  • Attack vector: Network (AV:N), low attack complexity (AC:L).
  • Impact: Successful exploitation — where a suitable POP chain is available — can lead to remote code execution (RCE), SQL injection, path traversal, and denial of service. CVSS rates Confidentiality, Integrity, and Availability impact each as High.

Affected software

  • Fusion Builder (WordPress plugin by ThemeFusion) — all versions ≤ 3.15.4

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 Fusion Builder to version 3.15.5 or later, which contains the vendor-provided fix as confirmed by the CVE record and Patchstack advisory.
  • If immediate patching is not feasible, consider applying virtual patching rules via a web application firewall (WAF) and restricting external access to WordPress AJAX endpoints as a temporary measure.

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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