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CVE-2021-3199

ONLYOFFICE Docs Server Path Traversal

9.8 CRITICALActively exploited (CISA KEV)Public exploitEPSS 19.4%
  1. Published26 Jan 2021
  2. Added to CISA KEV8 Oct 2026
  3. Remediation due11 Oct 2026
Actively exploited (CISA KEV)

ONLYOFFICE Docs contains a path traversal vulnerability that can occur when JWT is used, via a /.. sequence in an image upload parameter and could allow for remote code execution.

Added to KEV: 8 Oct 2026Federal remediation due: 11 Oct 2026

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 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Onlyoffice Document Server< 5.6.3

Remediation

Fixed in
Onlyoffice Document Server≥ 5.6.3

References

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Frequently asked

Is CVE-2021-3199 being actively exploited?

Yes. CVE-2021-3199 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 8 Oct 2026.

How severe is CVE-2021-3199?

CVE-2021-3199 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 19.4% probability of exploitation.

Which products are affected by CVE-2021-3199?

Affected products include Onlyoffice Document Server.

How do I fix CVE-2021-3199?

Upgrade affected software to a fixed version, for example Onlyoffice Document Server 5.6.3 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-3199 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.