CVE-2026-53909CWE-434

Arbitrary File Upload in MCO

Medium · published July 1, 2026

CVSS v4.0
5.3
EPSS
0%
Percentile
32.5
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
5.3 · MEDIUM
Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
EPSS
0.00394 · 32.5th percentile
Weakness
CWE-434 · Unrestricted Upload of File with Dangerous Type
Published
2026-07-01T11:59Z
EPSS history
Timeline
  • 01 JUL 11:59Z
    Arbitrary File Upload in MCO
    cvelistv5