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CVE-2026-81891 – Remote Code Execution via ZIP-Extraction MIME Filter Bypass – elFinder < 2.1.70

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Summary

CVE-2026-81891 is an unrestricted file upload vulnerability (CWE-434) in Studio-42 elFinder, the widely embedded open-source web file manager. Flawed MIME-type normalization during ZIP extraction lets an attacker with ZIP upload permission plant PHP-executable files in a web-accessible directory, leading to remote code execution. The flaw is rated HIGH severity (CVSS 8.1) and affects all elFinder versions prior to 2.1.70.

Technical details

  • Root cause: checkExtractItems() in php/elFinderVolumeDriver.class.php calls mimetypeInternalDetect() without passing the result through mimeTypeNormalize().
  • The extensions .phtml, .phar, .php5, and .php3 are absent from mime.types, so the staticMimeMap entries mapping them to text/x-php are never applied.
  • As a result, allowPutMime() permits extraction of these files even when the uploadDeny configuration blocks text/x-php.
  • Attack vector: network-based; the attacker needs ZIP file upload capability within elFinder but no additional authentication beyond that.
  • Impact: extraction of PHP-executable files into a web-accessible files/ directory, resulting in remote code execution when the server processes those files.

Affected software

  • Studio-42 elFinder versions prior to 2.1.70

Severity

  • CVSS v3.1 Base Score: 8.1 (HIGH)
  • Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: upgrade elFinder to version 2.1.70 or later, which fixes the MIME normalization logic in the extraction path.
  • If immediate patching is not possible: restrict or disable ZIP upload/extraction functionality for untrusted users, tighten uploadDeny/uploadAllow configurations, and ensure the upload/files directory is not configured to execute PHP (e.g., via web server configuration disabling script execution in that path).

References

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