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CVE-2026-77992 – Unauthenticated Code Injection (RCE) – Fabrik for Joomla 1.0.0 through 4.7.1

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Summary

CVE-2026-77992 is a critical code injection vulnerability in the calc element of Fabrik, an application-builder extension for Joomla. The flaw is a heredoc terminator breakout that lets an unauthenticated attacker break out of a PHP heredoc block used to evaluate calc-element expressions, because the extension’s onUpdateComment endpoint performs no access checks. It is rated CVSS 9.5 (Critical) and is remotely exploitable with no authentication or user interaction.

Technical details

  • Root cause: Fabrik’s calc element evaluates a site-builder-defined PHP expression to compute a field value, embedding request/row data inside a PHP heredoc block; the heredoc terminator can be broken out of, allowing injected PHP syntax to be generated and executed (CWE-94, Improper Control of Generation of Code).
  • Trigger condition: reachable through the onUpdateComment endpoint in com_fabrik, which lacks any access control checks, so a request can reach the vulnerable code path without authentication.
  • Attack vector: network-based, exploitable by an anonymous, unauthenticated visitor with no user interaction required.
  • Impact: high confidentiality, integrity, and availability impact — consistent with arbitrary PHP code execution on the affected Joomla site.

Affected software

  • Fabrik extension for Joomla, versions 1.0.0 through 4.7.1
  • Fixed in Fabrik 4.7.2

Severity

  • CVSS v4.0 Base Score: 9.5 (Critical)
  • Vector: CVSS:4.0/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 Fabrik to version 4.7.2 or later.
  • If immediate patching is not possible: restrict or disable public access to the affected front-end calc-element/comment-update functionality (e.g., via web server or WAF rules blocking unauthenticated requests to the onUpdateComment endpoint) until the update can be applied, and monitor Joomla sites running Fabrik for suspicious PHP execution or unexpected calc-element behavior.

References

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