---
title: "CVE-2021-3199: ONLYOFFICE Docs Server Path Traversal Vulnerability"
url: https://erroneo.us/security/cve/CVE-2021-3199/
description: "CVE-2021-3199 (ONLYOFFICE Docs): Exploited in the wild (CISA KEV). Directory traversal with remote code execution can occur in /upload in ONLYOFFICE…"
type: vulnerability-record
section: "Security Digest"
date_published: 2021-01-22
date_modified: 2026-10-09
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2021-3199"
kev: true
cvss: 9.8
epss: 0.20136
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2021-3199: ONLYOFFICE Docs Server Path Traversal Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run ONLYOFFICE Docs. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-10-08, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-10-11 ; treat that as the outer limit, not the target.
- EPSS 20.1% , percentile 97: FIRST’s model estimates a 20.1% chance of exploitation activity in the next 30 days, higher than 97% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Check exposure. ONLYOFFICE Docs CVE-2021-3199: Old Upload RCE Now in KEV — Only Document Server installs older than 5.6.3, a release from August 2020, are at risk, but any you find should be treated as exposed and upgraded or pulled offline today.

## What it is

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.

## Affected products (CVE record)

- n/a n/a: see advisory

## Severity

- CISA-ADP CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: added 2026-10-08; federal due date 2026-10-11. Known ransomware use: Unknown.
- CISA 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 20.14% probability of exploitation activity in the next 30 days; percentile 97.

## Sources

- [Listed in CISA KEV notes (github.com)](https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563)
- [CVE.org record CVE-2021-3199](https://www.cve.org/CVERecord?id=CVE-2021-3199)
- [NVD entry CVE-2021-3199](https://nvd.nist.gov/vuln/detail/CVE-2021-3199)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3199)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk)
- [github.com](https://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.py)
- [github.com](https://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.py)

---
Source page: https://erroneo.us/security/cve/CVE-2021-3199/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt