MaxUpload <= 1.4.0 - Unauthenticated Arbitrary File Upload via 'resumableFilename' Parameter
Strategic Overview
- Status
- Unpatched
- Affected Version
<= 1.4.0- CVSS
- 8.8High
- Weakness type
- CWE-434 · Unrestricted Upload of File with Dangerous Type
- CVE
CVE-2026-15965
At a glance
CVE-2026-15965 is a high-severity Unrestricted Upload of File with Dangerous Type vulnerability in the MaxUpload WordPress plugin, affecting versions <= 1.4.0. It carries a CVSS score of 8.8 (reachable over the network; low attack complexity; high confidentiality, integrity, availability impact). Exploitation requires no authentication. No fixed release has been reported yet; treat installations running this software as exposed. Disclosed August 2026, reported by JIWOONG LEE (kimchunbok).
Vulnerability Overview
The MaxUpload – Big File Uploads – Increase Maximum File Upload Size plugin for WordPress is vulnerable to Arbitrary File Upload in all versions up to, and including, 1.4.0 via the handle_upload function. This is due to a filename-validation mismatch in the handle_upload function where extension and MIME checks are applied to the uploaded chunk's filename but not to the final assembled filename derived from the resumableFilename parameter. This makes it possible for unauthenticated attackers to upload files that may be executable, which makes remote code execution possible.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user. A successful exploit has high impact on confidentiality, integrity, availability — full site compromise territory.
CWE-434: Unrestricted Upload of File with Dangerous Type
Reaching this weakness in MaxUpload <= 1.4.0 takes no account at all. An unrestricted file upload lets a caller store a file whose type or destination the application does not properly constrain.
If an uploaded file lands anywhere the server will execute, the flaw becomes remote code execution and the site should be treated as fully compromised. No fixed build of this plugin is recorded for MaxUpload yet, so installs running <= 1.4.0 stay exposed until the vendor ships one.
Remediation
No known patch available. Please review the vulnerability's details in depth and employ mitigations based on your organization's risk tolerance. It may be best to uninstall the affected software and find a replacement.
How does WordSec protect against this?
Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. No patched version is recorded yet, which is the case where a filtering layer matters most, because there is nothing to update to.
- Firewall
- Scanner
- Login Security
External References
Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C