CVE-2021-3199: ONLYOFFICE Docs Server Path Traversal Vulnerability
CVSS 9.8 · Critical⚠ Actively exploited (CISA KEV)
9.8
CVSS score
Critical
Severity
Active
CISA KEV
No
Ransomware use
Oct 11, 2026
Patch deadline
⚠ Exploited in the wild. CISA added CVE-2021-3199 to its Known Exploited Vulnerabilities catalog on Oct 8, 2026, with a federal patch deadline of Oct 11, 2026 — meaning attackers are actively using it. If you run the affected software, patch it immediately.
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.
Details
AffectedONLYOFFICE · Docs
WeaknessCWE-22
CVSS base score9.8 (Critical)
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HPublishedJan 26, 2021
Added to CISA KEVOct 8, 2026
Federal patch deadlineOct 11, 2026
Known ransomware useNot documented
Frequently asked questions
Is CVE-2021-3199 being actively exploited?
Yes — CISA lists CVE-2021-3199 in its Known Exploited Vulnerabilities (KEV) catalog, so it is confirmed exploited in the wild. Patch it as a priority.
What does CVE-2021-3199 affect?
CVE-2021-3199 affects ONLYOFFICE · Docs.
How do I fix CVE-2021-3199?
Apply the vendor’s patch for the affected software. The federal patch deadline was Oct 11, 2026. Then check whether your personal data was exposed in any related breach.
References
- github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebea
- github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.py
- github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFil
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3199