Exploited vulnerability · CISA KEV

Is CVE-2021-3199 exploited? Yes: in CISA KEV since 8 Oct 2026

Gociux · ONLYOFFICE Docs · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-3199, ONLYOFFICE Docs Server Path Traversal Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 8 Oct 2026, 2085 days after it was published. It affects ONLYOFFICE Docs. If you run it, CISA's required action is: 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.

What it is

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.

What to do

1. Check whether you run it. Look for Docs in your asset inventory, including appliances and cloud images. Stack check lists every exploited ONLYOFFICE CVE at once.
2. Apply the fix. 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.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 22 Jan 2021.
4. Get told next time. Email alerts when CISA adds a CVE for ONLYOFFICE.

References

• github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d
• nvd.nist.gov/vuln/detail/CVE-2021-3199

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in October 2026 · act-now radar.