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CVE-2026-48939 – Unauthenticated File Upload RCE – iCagenda Extension for Joomla up to 4.0.7

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Summary

CVE-2026-48939 is a critical unauthenticated arbitrary file upload vulnerability in the iCagenda events calendar extension for Joomla, affecting all releases from 1.0.0 through 4.0.7. The flaw allows any unauthenticated internet visitor to upload and execute a PHP web shell through the extension’s public event submission form, resulting in full remote code execution (RCE) on the underlying server. This vulnerability carries a CVSS 4.0 score of 10.0 and was being actively exploited in the wild before the patch was released on June 15, 2026.

Technical details

  • Root cause: The event submission form’s file attachment feature lacked file extension validation and did not invoke Joomla’s built-in security helpers (MediaHelper allow-list). The processing controller accepted any file extension supplied by the requester and wrote the uploaded file directly to a web-accessible directory. Access controls were only enforced at the view layer, not at the controller level, making them trivially bypassable by posting directly to the processing endpoint.
  • Trigger conditions: An attacker harvests a form token from any public iCagenda event submission page, then POSTs a malicious .php file directly to the processing controller — all without any authentication or user interaction.
  • Attack vector: Fully network-accessible (AV:N); zero privileges required (PR:N); no victim interaction needed (UI:N); attack complexity is low (AC:L).
  • Impact: Successful exploitation writes an executable PHP web shell into the images/icagenda/frontend/attachments/ directory, granting full server-side code execution under the web server process. This enables complete host compromise, data exfiltration, and lateral movement.
  • Active exploitation: Automated exploitation was observed in the wild prior to patch availability, with attacking clients identifying themselves via the user-agent string icagenda-batch/1.0.
  • Indicator of compromise: Unexpected .php files present under images/icagenda/frontend/attachments/ are a strong indicator of exploitation.

Affected software

  • iCagenda extension for Joomla, versions 1.0.0 through 3.9.14
  • iCagenda extension for Joomla, versions 4.0.0 through 4.0.7

Severity

CVSS 4.0 Score: 10.0 (Critical)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:A/AU:Y/U:Red

Mitigation and recommended actions

  • Immediate — upgrade: Update to iCagenda 4.0.8 (released June 15, 2026), which introduces proper file type validation via Joomla’s MediaHelper allow-list and relocates access enforcement to the controller layer.
  • If immediate patching is not feasible: Disable the file attachment feature on the iCagenda event submission form, or restrict unauthenticated public access to the form processing endpoint at the web server or WAF level until the patch can be applied.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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