CVE-2021-3199
ONLYOFFICE Docs Server Path Traversal Vulnerability
ONLYOFFICE Docs
Directory traversal with remote code execution can occur in /upload in ONLYOFFICE Document Server before 5.6.3, when JWT is used, via a /.. sequence in an image upload parameter.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 8 October 2026. US federal agencies were required to remediate it by 11 October 2026.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 20.1%, which is higher than 97.5% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Frequently asked questions
Is CVE-2021-3199 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2021-3199.
What does CVE-2021-3199 affect?
CVE-2021-3199 affects ONLYOFFICE Docs. Directory traversal with remote code execution can occur in /upload in ONLYOFFICE Document Server before 5.6.3, when JWT is used, via a /.. sequence in an image upload parameter.
How severe is CVE-2021-3199?
CVE-2021-3199 is rated CRITICAL with a CVSS base score of 9.8. EPSS puts the probability of exploitation in the next 30 days at 20.1%, higher than 97.5% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 11 October 2026.
How should organisations respond to CVE-2021-3199?
Apply the vendor patch for ONLYOFFICE Docs as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.