CVE-2026-53909 Arbitrary File Upload in MCO

Medium 5.3 Published 1 Jul 2026 Updated 1 Jul 2026

An authorized low-privileged attacker can bypass client-side checks to upload arbitrary file types, potentially leading to code execution or data modification.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-53909?

CVE-2026-53909 is a medium-severity vulnerability in MyComplianceOffice MCO, published on 1 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

MCO does not correctly validate types of uploaded files. File upload validation functionality relies only on client-side checks, which can be bypassed. An authorized, low-privileged attacker can upload files with arbitrary types to the server.

Because vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 25.3.3.1 but may also affect other versions.

Weakness: CWE-434

Which versions are affected by CVE-2026-53909?

It affects 1 product.

Products include Mycomplianceoffice Mycomplianceoffice.

How do I fix CVE-2026-53909?

No fix has been published for CVE-2026-53909 yet. Limit exposure of the affected software until one is available.

Is CVE-2026-53909 being exploited?

There is no known exploitation of CVE-2026-53909 in the wild and no public exploit code.

Sources

Also known as GHSA-5v97-p7p8-r448.