CVE-2021-25830: ONLYOFFICE Document Server

Critical severity, CVSS 9.8. EPSS: 11.8% chance of exploitation in the next 30 days.

A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.2.0.236-v5.6.4.13. An attacker must request the conversion of the crafted file from DOCT into DOCX format. Using the chain of two other bugs related to improper string handling, an attacker can achieve remote code execution on DocumentServer.

Affected products

• ONLYOFFICE Document Server: from 4.2.0.236, up to and including 5.6.4.13

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