CVE-2021-3199

ONLYOFFICE Docs remote code execution, confirmed exploited in the wild.

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.

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30%chance of exploitation in the next 30 days (EPSS), 98th percentile

8 Octadded to CISA's Known Exploited Vulnerabilities list, 2026

11 Octfederal remediation deadline, already passed

Passedpast the deadline: patch now

CISA's name for it	ONLYOFFICE Docs Server Path Traversal Vulnerability
Vendor and product	ONLYOFFICE · Docs
Type	remote code execution · CWE-22
Exploited	Confirmed by CISA listed 8 October 2026
Likelihood	one of the most likely to be exploited of every vulnerability tracked
Deadline	11 October 2026 · already passed
Used in ransomware	Not reported
Advisories	github.com ↗ · www.cisa.gov ↗ · www.cisa.gov ↗ · nvd.nist.gov ↗

What to do

Three steps, in this order

Step 1

Patch to the fixed version the vendor names, today if the product faces the internet.

Step 2

Until it is patched, take the affected service off the internet or put it behind a VPN or allow-list.

Step 3

Look for signs it was already used: new accounts, web shells, unexpected processes and outbound connections since the date it was listed.

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.

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.

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Questions

CVE-2021-3199 in short

Is CVE-2021-3199 being exploited?

Yes. CISA added CVE-2021-3199 to its Known Exploited Vulnerabilities catalogue on 8 October 2026, which it does only on evidence of exploitation in the wild.

What is the CISA deadline for CVE-2021-3199?

US federal agencies must remediate it by 11 October 2026. Everyone else should treat that date as the latest safe point to patch an internet-facing system.

How likely is CVE-2021-3199 to be exploited in the next 30 days?

FIRST's Exploit Prediction Scoring System gives it 30%, the 98th percentile of every CVE it scores.

How do I fix CVE-2021-3199?

Patch to the fixed version the vendor names, today if the product faces the internet. Until it is patched, take the affected service off the internet or put it behind a VPN or allow-list. Look for signs it was already used: new accounts, web shells, unexpected processes and outbound connections since the date it was listed.

Sources: CISA Known Exploited Vulnerabilities catalogue (released 10 November 2026) and FIRST EPSS. Page compiled automatically by SAK T.L.M, the threat-intelligence tool of SAK T.E.C, on 13 November 2026.