CVE-2021-3199
CriticalExploitedPublic exploitDirectory traversal with remote code execution can occur in /upload in ONLYOFFICE Document Server before 5.6.3, when JWT is used, via a /..
Published Jan 26, 2021 · Updated Oct 11, 2026
Key Facts
Patch immediately- CVE-2021-3199 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Document Server (Onlyoffice).
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Oct 8, 2026. Public exploit code is available.
- EPSS estimates a 20% probability of exploitation in the next 30 days.
- Fixed versions are available, including Document Server 5.6.3.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
20%
Higher than 97.4% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-3199 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
Description
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.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Oct 8, 2026 | Oct 11, 2026 | Not reported |
| Industry KEV feed | Oct 8, 2026 | Oct 11, 2026 | Not reported |
| CIRCL KEV | Oct 8, 2026 | Oct 11, 2026 | Not reported |
| ENISA EUVD | Oct 8, 2026 | n/a | Not reported |
Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Affected Products
1 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Document ServerOnlyoffice | See advisory | 5.6.3 |
Patched Releases
Document Server
5.6.3
Timeline
Publicly disclosed
Jan 26, 2021
Added to CISA KEV
Oct 8, 2026
Added to Industry KEV feed
Oct 8, 2026
Added to CIRCL KEV
Oct 8, 2026
Added to ENISA EUVD
Oct 8, 2026
Last updated
Oct 11, 2026
Weakness Type
- CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
References
- advisoryhttps://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563
- exploithttps://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.py
- exploithttps://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.py
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
FAQ
Common Questions.
Directory traversal with remote code execution can occur in /upload in ONLYOFFICE Document Server before 5.6.3, when JWT is used, via a /..
Affected: Document Server (Onlyoffice). The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Oct 8, 2026.
Yes. It was added on Oct 8, 2026 with a federal remediation due date of Oct 11, 2026.
Public exploit code is available.
Fixed versions are available, including Document Server 5.6.3.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Is CVE-2021-3199 Running On Your Attack Surface?
Brandefense maps vulnerabilities like this one to your internet-facing assets and tells you exactly where to patch.
Request A Demo