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CVE-2026-18431 – Unauthenticated Remote Code Execution via Arbitrary File Write – Avada Theme (≤ 7.1

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Summary

CVE-2026-18431 is a critical arbitrary file write vulnerability affecting the Avada WordPress theme (versions up to and including 7.16) when used together with the Fusion Builder plugin (versions up to and including 3.16). Unauthenticated attackers can exploit a chain of authorization and input validation weaknesses spanning both components to write attacker-controlled files to the server, which can then be used to create and execute arbitrary PHP code. The flaw is rated CRITICAL with a CVSS v3.1 base score of 9.8.

Technical details

  • Root cause: a combination of missing authorization (CWE-862) and insufficient input validation across the Avada theme and its bundled Fusion Builder plugin.
  • Trigger conditions: both Avada and Fusion Builder must be installed and active, and certain administrator-authored content must be present on the site.
  • Attack vector: network-based, requires no authentication and no user interaction (AV:N/AC:L/PR:N/UI:N).
  • Impact: attacker-controlled files can be written to the server; combined with the ability to create and execute PHP files, this leads to remote code execution and full site compromise (confidentiality, integrity, and availability impact all rated High).

Affected software

  • Avada (Fusion) Builder plugin: versions ≤ 3.16
  • Avada | Website Builder for WordPress & WooCommerce (theme): versions ≤ 7.16
  • Exploitation requires both components to be installed and active together.

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 Avada theme and Fusion Builder plugin to the latest available versions beyond 7.16/3.16. ThemeFusion has released Avada 7.16.1, which addresses a remote code execution vulnerability; sites should apply this update (and any accompanying Fusion Builder update) immediately.
  • If patching cannot be performed immediately: restrict or monitor unauthenticated access to Avada/Fusion Builder front-end endpoints, and review recently created/modified files (particularly PHP files) in the WordPress upload and theme/plugin directories for signs of compromise.
  • Review administrator-authored content that could be leveraged as part of the exploitation chain, and audit site file integrity following any suspected exposure.

How IONIX identifies potentially affected assets

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

  • Raw response body: fusionJSVars

References

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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

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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  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
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