CVE-2021-3199
ONLYOFFICE Docs Server Path Traversal Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 11 October 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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.
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 30.24% probability · 98th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Listed 8 October 2026 · due 11 October 2026
- Weakness
- CWE-22
- Affected
- onlyoffice/document server
- Source
- cve@mitre.org
EPSS moved from 14.5% on 9 October 2026 to 30.2% on 26 October 2026. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”.
CISA notes
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. This vulnerability could affect an open-source component, third-party library, protocol, or proprietary implementation that could be used by different products. For more information, please see: ; https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2021-3199
References
- https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563Release Notes, Third Party Advisory
- https://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.pyExploit, Third Party Advisory
- https://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.pyExploit, Third Party Advisory
- https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563Release Notes, Third Party Advisory
- https://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.pyExploit, Third Party Advisory
- https://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.pyExploit, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3199US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.