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CVE-2026-4357 – Unauthenticated Arbitrary File Upload (RCE) – Embed HTML5 Game WordPress Plugin ≤ 1.

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Summary

CVE-2026-4357 is a critical unrestricted file upload vulnerability (CWE-434) in the Embed HTML5 Game WordPress plugin, affecting all versions through 1.3. The plugin fails to enforce access control or file-type restrictions on its upload functionality, allowing unauthenticated attackers to upload arbitrary PHP files. Successful exploitation can lead to full remote code execution and complete compromise of the affected WordPress site.

Technical details

  • Root cause: The plugin does not properly restrict who can upload files or what file types can be uploaded through its upload handler.
  • Trigger conditions: No authentication or user interaction is required; the vulnerable upload endpoint is reachable by any remote, unauthenticated user.
  • Attack vector: Network — an attacker sends a crafted upload request directly to the affected WordPress site.
  • Impact: Attackers can upload PHP web shells/backdoors, resulting in remote code execution, and complete loss of confidentiality, integrity, and availability of the site.

Affected software

  • Embed HTML5 Game WordPress plugin, versions 0 through 1.3 (all known releases)

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: No patched version is currently available. Deactivate and remove the Embed HTML5 Game plugin from all WordPress installations until a fix is released.
  • If removal is not immediately possible: Restrict or block access to the plugin’s upload endpoint at the web server or WAF layer, monitor for newly created PHP files in upload directories, and review site files for unauthorized web shells or backdoors.

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/embed-html5-game/

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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