The US Cybersecurity and Infrastructure Security Agency (CISA) added CVE-2021-3199, a ONLYOFFICE Docs Server Path Traversal Vulnerability, to its Known Exploited Vulnerabilities (KEV) catalog on October 8, 2026. CISA adds a flaw to the catalog when it has reliable evidence that attackers are exploiting it in the wild.
What CISA says
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.
— CISA KEV catalog entry for CVE-2021-3199
Key facts
| CVE | CVE-2021-3199 |
|---|---|
| Vendor / product | ONLYOFFICE Docs |
| Added to KEV | October 8, 2026 |
| Federal deadline | October 11, 2026 |
| Known ransomware use | Unknown |
| Weakness (CWE) | CWE-22 |
| CISA forensic triage | Yes |
| CVSS base score (NVD) | 9.8 Critical |
| CVSS vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
Who has to act, and by when
US federal civilian executive branch agencies are required to remediate the vulnerability by October 11, 2026. CISA urges all organizations to prioritize KEV-listed flaws as part of their vulnerability management.
CISA’s required action for this entry:
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.
References
- CISA Known Exploited Vulnerabilities Catalog https://www.cisa.gov/known-exploited-vulnerabilities-catalog
- NIST NVD — CVE-2021-3199 https://nvd.nist.gov/vuln/detail/CVE-2021-3199
- github.com https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563
- www.cisa.gov https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- www.cisa.gov https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk