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CVE-2026-61900 – Unauthenticated File Upload leading to RCE – jDownloads extension for Joomla 4.1…

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Summary

CVE-2026-61900 is a critical unauthenticated file upload vulnerability in the jDownloads download-manager extension for Joomla (versions 4.1.0 through 4.1.5), leading to full Remote Code Execution on the server. Published on July 20, 2026, it carries a CVSS 4.0 score of 10.0 (Critical) — the maximum possible — reflecting that exploitation requires no authentication, no user interaction, and no special conditions over the network. A patch is available in jDownloads 4.1.6, released July 18, 2026.

Technical details

  • Root cause: A standalone file upload handler (administrator/components/com_jdownloads/assets/upload/upload-handler.php) was accidentally included in the jDownloads release packages for versions 4.1.0–4.1.5. This script is a leftover test artifact: it contains no Joomla _JEXEC guard, no session check, no CSRF token validation, and no permission check of any kind, making it fully accessible to unauthenticated internet users.
  • Trigger conditions: Any unauthenticated attacker can send an HTTP POST request directly to the exposed handler endpoint and upload arbitrary files. The handler’s built-in extension allowlist blocks direct .php uploads by default but permits archives, images, documents, and executable file types (e.g., .exe, .msi). RCE is achievable on servers with Apache AddHandler or mod_mime secondary-extension misconfigurations, or where an administrator has expanded the allowed upload types to include server-executable extensions.
  • Attack vector: Remote, unauthenticated, network-accessible — no privileges or user interaction required (CVSS: AV:N/AC:L/AT:N/PR:N/UI:N).
  • Impact: Full compromise of confidentiality, integrity, and availability on the vulnerable system and potentially connected systems (CVSS: VC:H/VI:H/VA:H/SC:H/SI:H/SA:H). The vulnerability is classified as CWE-434 (Unrestricted Upload of File with Dangerous Type).

Affected software

  • jDownloads extension for Joomla 4.1.0
  • jDownloads extension for Joomla 4.1.1
  • jDownloads extension for Joomla 4.1.2
  • jDownloads extension for Joomla 4.1.3
  • jDownloads extension for Joomla 4.1.4
  • jDownloads extension for Joomla 4.1.5
  • Earlier 4.0.x releases are not affected — the vulnerable upload handler is absent from version 4.0.52 and below.

Severity

  • CVSS 4.0 Base 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

Mitigation and recommended actions

  • Immediate — upgrade to jDownloads 4.1.6, released July 18, 2026. This version removes the vulnerable upload handler and all associated leftover test artifacts, and applies enhanced clean-up of any residual test_uploads directory upon installation.
  • After upgrading, review your server’s upload and access logs for any suspicious POST requests to administrator/components/com_jdownloads/assets/upload/ to assess whether exploitation was attempted prior to patching.
  • If immediate patching is not possible, block public HTTP access to administrator/components/com_jdownloads/assets/upload/ at the web server or WAF level as an interim measure.

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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