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CVE-2026-77138 – Unauthenticated RCE via PHP Object Injection – TYPO3 “HTML5 Video Player vs. Powerm

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Summary

CVE-2026-77138 is a critical insecure deserialization vulnerability (CWE-502) in the TYPO3 CMS third-party extension "HTML5 Video Player vs. Powermail" (lochmueller/html5videoplayer-powermail). The extension passes an attacker-controlled cookie value directly into PHP’s unserialize() function without validation, allowing an unauthenticated remote attacker to trigger PHP Object Injection and achieve remote code execution on the underlying TYPO3 server. The issue carries a CVSS v4.0 base score of 9.3 (Critical) and affects all released versions of the extension.

Technical details

  • Root cause: The extension reads a value from a client-supplied cookie and passes it unsanitized to PHP’s native unserialize() function.
  • Trigger conditions: No authentication or user interaction is required; an attacker simply sends an HTTP request with a crafted, malicious serialized PHP object in the cookie value to a TYPO3 site running the vulnerable extension.
  • Attack vector: Network-based (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction required (UI:N).
  • Impact: Successful exploitation results in PHP Object Injection, which can be leveraged (depending on available "POP chain" classes/gadgets in the application) to achieve arbitrary remote code execution, along with high impact to confidentiality, integrity, and availability of the affected system.

Affected software

  • TYPO3 extension HTML5 Video Player vs. Powermail (html5videoplayer_powermail / lochmueller/html5videoplayer-powermail)
  • Affected versions: 0 through 0.2.1 (all publicly released versions)

Severity

  • CVSS v4.0 Base Score: 9.3 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: No patched version of this extension exists. Per the official TYPO3 security advisory (TYPO3-EXT-SA-2026-014), the extension is outdated and unmaintained.
  • Recommended action: Uninstall and completely delete the extension folder from the TYPO3 installation. Search the TYPO3 Extension Repository (TER) for an actively maintained alternative extension providing equivalent functionality.
  • Network mitigation (if immediate removal is not possible): Block or strip the specific cookie used by the extension at a WAF/reverse proxy layer, and restrict/monitor inbound traffic to the affected TYPO3 instance until the extension can be removed.

References

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