Vulnerability

CVE-2021-3199

Critical· 9.8KEVCVSS9.8EPSS20%

.rules3/5

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.

Threat signal

100/100

Severe

Severity

critical

CVSS

9.8

EPSS

20%

Active

KEV

CISA KEV — actively exploited

11d overdue

AffectedONLYOFFICE — Docs

Added to KEV

2026-10-08

Federal patch due (BOD 22-01)

2026-10-11

Required action (CISA verbatim)

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.

Vendor advisory + references

CISA description: “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.”

CVSS

v3.1via NVDOpen in FIRST calculator →

9.8/ 10CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack VectorNetworkExploitable remotely over the internet — no local access needed.
Attack ComplexityLowNo special conditions — exploit works reliably.
Privileges RequiredNoneUnauthenticated — no credentials needed.
User InteractionNoneFully automated — no victim action needed.
ScopeUnchangedImpact contained to the vulnerable component.
Confidentiality ImpactHighTotal disclosure of sensitive data.
Integrity ImpactHighTotal compromise of integrity — full data modification possible.
Availability ImpactHighTotal loss of availability — full DoS possible.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

20.1%

probability of exploitation in next 30 days

p97

higher than 97% of all CVEs

9-day trend↑ 0.8pp

Above the FIRST 'patch on a priority schedule' threshold.

Vendor VEX

No VEX statements published for CVE-2021-3199. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.

SSVCAct

Active exploitation with total impact on essential/support systems

exploitation: active
automatable: yes
impact: total
mission: support

Lifecycle

2021-01-26Published
2026-10-08Added to CISA KEVransomware: Unknown
2026-10-08Vendor advisory · cisa-aaaa26-281a — Chinese Government-linked Cyber Threat Actors Combine Automated and Hands-on Hac
2026-10-09Last modified2 sources
2026-10-11Federal patch due (BOD 22-01)

Entity graph

2 nodes · 1 edges · click to pivot

CVEActorVendor advisoryIOCNews

Vendor advisories

cisa-aaaa26-281aChinese Government-linked Cyber Threat Actors Combine Automated and Hands-on Hacking Tools to Steal Sensitive Data

CVE-2021-3199

CISA KEV — actively exploited

CVSS

EPSS

Vendor VEX

Lifecycle

Entity graph

Vendor advisories

References

CVE-2021-3199

CISA KEV — actively exploited

CVSS

EPSS

Vendor VEX

Lifecycle

Entity graph

Vendor advisories

References