CVE-2021-3199
CRITICAL 9.8 KNOWN EXPLOITED ALL-YEARSDirectory 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.
Confirmed exploited in the wild — in CISA KEV since 2026-10-08. Patch or mitigate now.
Exploitation likelihood
30.2%chance of exploitation in 30 days · 98th percentile
Impact if exploited
9.8CVSS 3.1 · CRITICAL · ADP
- ConfidentialityHigh
- IntegrityHigh
- AvailabilityHigh
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ✓Privileges: No account or privileges required
- ✓User interaction: No user interaction needed
- ✓Complexity: No special conditions — reliably repeatable
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
Search for new PoCs
Search GitHub now — results may be empty or unverified.
Tracked sources are checked weekly for the full archive, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.
Weakness (CWE)
- CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References and research data (JSON)
Additional exploitation reports
Source-specific reports, separate from CISA KEV. Repeated observations from one source are not independent confirmations.
- VulnCheck KEV · 2026-10-08T00:00:00Z
Source guidance: 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.
Source ransomware assessment: Unknown
VulnCheck KEV · CVE-2021-3199 · Updated 2026-10-08T00:00:00Z - VulnCheck KEV · 2026-10-08T00:00:00ZVulnCheck KEV · CVE-2021-3199
VulnCheck KEV · CVE-2021-3199
Known Affected Software Configurations
| Vendor | Product | Version range |
|---|---|---|
| Onlyoffice | Document Server | < 5.6.3 |
All CVSS metrics
- CRITICAL 9.8 v3.1 · ADP Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - CRITICAL 9.8 v3.1 · NVD Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - HIGH 7.5 v2.0 · NVD Primary
AV:N/AC:L/Au:N/C:P/I:P/A:P
References
Exploit-tagged references (not proof of a PoC)
- https://github.com/nola-milkin/poc_exploits/blob/master/CVE-2021-3199/poc_uploadImageFile.py CVE record · mitre · Updated 2022-03-21T20:03:15.000Z
CVE record · CVE · Updated 2024-08-03T16:45:51.411Z
NVD · CVE-2021-3199 · Updated 2026-10-09T14:20:47.350 - https://github.com/moehw/poc_exploits/tree/master/CVE-2021-3199/poc_uploadImageFile.py CVE record · mitre · Updated 2022-03-21T20:03:15.000Z
CVE record · CVE · Updated 2024-08-03T16:45:51.411Z
NVD · CVE-2021-3199 · Updated 2026-10-09T14:20:47.350
Advisories
- https://github.com/ONLYOFFICE/DocumentServer/blob/903fe5ab7a275bd69c3c3346af2d21cf87ebeabf/CHANGELOG.md#563 CVE record · mitre · Updated 2022-03-21T20:03:15.000Z
CVE record · CVE · Updated 2024-08-03T16:45:51.411Z
NVD · CVE-2021-3199 · Updated 2026-10-09T14:20:47.350 - https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3199 CVE record · CISA-ADP · Updated 2026-10-09T03:55:31.111Z
NVD · CVE-2021-3199 · Updated 2026-10-09T14:20:47.350 - https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-26539 EUVD · EUVD-2021-26539
- https://vulncheck.com/kev VulnCheck KEV · CVE-2021-3199 · Updated 2026-10-08T00:00:00Z
Technical & other
- https://www.cisa.gov/news-events/cybersecurity-advisories/aa26-281a VulnCheck KEV · CVE-2021-3199 · Updated 2026-10-08T00:00:00Z
- https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json VulnCheck KEV · CVE-2021-3199 · Updated 2026-10-08T00:00:00Z
Sources: NVD · CVE.org · All sources and attribution · EPSS