Critical 9.8Known exploited (CISA KEV)Published Jan 22, 2021

CVE-2021-3199Directory traversal with remote code execution can occur in /upload in ONLYOFFICE Document Server before 5.6.3, when JWT is used, via a /..

Updated under an hour ago (2026-10-19 04:00 UTC)

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It affects onlyoffice document_server. Add what you run to find out whether that includes you.

CISA lists it as known exploited since Oct 8, 2026; federal agencies had to remediate by Oct 11, 2026. Treat that date as your deadline.

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Exploited in the last 30 days

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: 9.8 CRITICAL (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-22
Known exploited: Added to CISA KEV Oct 8, 2026; federal remediation due Oct 11, 2026Apply 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.
EPSS (exploitation in the next 30 days): 19.35% (percentile 97)
Assigned by: mitre
NVD analysis: Analyzed
Record last updated: Oct 9, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

onlyoffice document_server onlyoffice:document_server	before 5.6.3	NVD

References

https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563x-refsource-confirm
https://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.pyx-refsource-misc
https://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.pyx-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.