# CVE-2021-3199 **CISA KEV** > As of 2026-10-09, CVE-2021-3199 is a CRITICAL-severity vulnerability, CVSS v3.1 9.8, EPSS 14.5% (96.5th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-10-08), with a US federal remediation deadline of 2026-10-11. Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2021-3199, most recently “ONLYOFFICE Docs (Document Server) Path Traversal Leading to Remote Code Execution (CVE-2021-3199) Exploited in the Wild”. **Last updated:** 2026-10-09 ## What is CVE-2021-3199? 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. The record classifies CVE-2021-3199 under weakness class [CWE-22](https://intel.threadlinqs.com/cwe/CWE-22). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. The identifier was first published 2087 days ago. ## Severity and exploitation probability - **CVSS v3.1 base score:** 9.8 — CRITICAL (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`) - **EPSS (FIRST):** 14.5% probability of exploitation in the next 30 days, higher than 96.5% of all scored CVEs - **CISA KEV:** Listed since 2026-10-08, federal remediation deadline 2026-10-11 - **Threadlinqs priority:** 9/10 — CISA KEV-listed, which Threadlinqs floors at 9 - **Published:** 2021-01-22, last modified 2026-10-09 ## Is CVE-2021-3199 being exploited? CISA added CVE-2021-3199 to the Known Exploited Vulnerabilities catalog on 2026-10-08, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-10-11 under BOD 22-01. Weaponised exploit code for CVE-2021-3199 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 52 in the Threadlinqs vulnerability feed. - [trickest/cve](https://github.com/trickest/cve/blob/main/2021/CVE-2021-3199.md) (trickest) ## Affected products and versions No affected-product or package list has been recorded for CVE-2021-3199 in the tracked sources. The vendor advisory and the references below are the authoritative statement of what is affected. ## How to fix CVE-2021-3199 Because CVE-2021-3199 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-10-11. No vendor patch reference has been recorded for CVE-2021-3199 in the tracked sources. Follow the references below for a fix, and treat any affected deployment as exposed until the vendor states otherwise. ## Threat activity tracking CVE-2021-3199 2 tracked threats in the Threadlinqs corpus reference CVE-2021-3199, either in the campaign’s CVE list or as an indicator on the campaign record. - [ONLYOFFICE Docs (Document Server) Path Traversal Leading to Remote Code Execution (CVE-2021-3199) Exploited in the Wild](https://intel.threadlinqs.com/threat/TL-2026-3076) — HIGH · 2026-10-09 - [Chinese Government-linked Actors Enabled by Integrity Technology Group Combine Automated and Hands-on Hacking Tools to Steal Sensitive Data (CISA AA26-281A)](https://intel.threadlinqs.com/threat/TL-2026-3054) — HIGH · 2026-10-08 ## Sources Enriched from CVE.org, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-10-10. **Vendor advisory and patch** - [github.com](https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563) **Other references** - [github.com](https://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.py) - [github.com (poc uploadImageFile)](https://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.py) Canonical: https://intel.threadlinqs.com/cve/CVE-2021-3199 Full detection coverage and IOCs for threats exploiting CVE-2021-3199 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp