ONLYOFFICE Docs Server Path Traversal
CVE-2021-3199 is a critical-severity improper limitation of a pathname to a restricted directory vulnerability in Document Server from OnlyOffice, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 5.6.3 as the first without the flaw, so updating Document Server to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on October 8, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Document Server to 5.6.3 or a later version.
- CISA's 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.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Onlyoffice | Document Server | before 5.6.3 | 5.6.3 |
Version data comes from NVD's product matching. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.1 | 9.8 | Critical | CISA (ADP) |
| CVSS 2.0 | 7.5 | High | NVD |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Limitation of a Pathname to a Restricted Directory
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
How developers prevent this class of flaw
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.
More Improper Limitation of a Pathname to a Restricted Directory vulnerabilities (CWE-22)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Record last changed materially (score, affected products, status or references).
- Deadline for US federal agencies to remediate, set by CISA.
References
Patches and release notes
- github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563Release Notes, Third Party Advisory
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3199US Government Resource
Technical write-ups (may include proof of concept)
- github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.pyExploit, Third Party Advisory
- github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.pyExploit, Third Party Advisory
Other vulnerabilities in Document Server
- 8.7 High severity
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 7.8 High severity
- 9.8 Critical severity
Recent Improper Limitation of a Pathname to a Restricted Directory vulnerabilities
- 7.5 High severity
- 7.8 High severity
- 7.5 High severity
- 6.5 Medium severity
- 9.8 Critical severity
- 7.5 High severity
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