CVE-2021-25833: ONLYOFFICE Document Server

Critical severity, CVSS 9.8. EPSS: 43.5% chance of exploitation in the next 30 days.

A file extension handling issue was found in [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting. Using this vulnerability, a remote attacker can obtain remote code execution on DocumentServer.

Affected products

• ONLYOFFICE Document Server: from 4.2.0.71, up to and including 5.6.0.21

Published 2021-03-01. Last modified 2026-06-17.