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CVE-2026-77136 – Server-Side Template Injection (SSTI) leading to potential RCE – TYPO3 Powermail Ex

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Summary

CVE-2026-77136 is a critical Server-Side Template Injection (SSTI) vulnerability in the "powermail" extension for TYPO3 CMS (package in2code/powermail). The extension passes the raw, unsanitized value of a form field configured as "This field contains the name of the sender" directly into a Fluid template for rendering, allowing an unauthenticated attacker to inject Fluid template syntax and execute arbitrary Fluid ViewHelpers. The issue is rated Critical severity and is reported to be under active exploitation.

Technical details

  • Root cause: Powermail renders the raw value of the "sender name" form field as Fluid template source without sanitization or escaping.
  • Trigger conditions: A Powermail form must have a field configured with the "This field contains the name of the sender" option; no authentication is required.
  • Attack vector: Network — an attacker submits a crafted form field value containing Fluid template/ViewHelper syntax through a normal, unauthenticated form submission.
  • Impact: Execution of arbitrary Fluid ViewHelpers can expose server configuration, environment variables, and application source code, and can lead to remote code execution on the underlying TYPO3 installation.

Affected software

  • in2code/powermail (TYPO3 extension) versions 10.9.2 and below
  • in2code/powermail versions 11.0.0 – 12.6.0
  • in2code/powermail versions 13.0.0 – 13.2.0

Severity

  • CVSS Score: 9.5 (Critical)
  • Vector (CVSS v4.0): AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Mitigation and recommended actions

  • Immediate: Upgrade in2code/powermail to version 10.9.3, 12.6.1, or 13.2.1 (or later), available via the TYPO3 extension manager or Packagist.
  • If no patch can be applied immediately: Disable the "This field contains the name of the sender" configuration option on all Powermail form fields until the update can be deployed. Given active exploitation, treat this as an urgent action.

References

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