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TI-2021-18199 Aliases CVE-2021-41380GHSA-789c-r6w2-66gw

RealVNC Viewer 6.21.406 allows remote VNC servers to cause a denial of service…

Priority LOW 31CWE-20Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
None · None · High
Fix status
No fix listed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA.

Summary

RealVNC Viewer 6.21.406 allows remote VNC servers to cause a denial of service (application crash) via crafted RFB protocol data. NOTE: It is asserted that this issue requires social engineering a user into connecting to a fake VNC Server. The VNC Viewer application they are using will then hang, until terminated, but no memory leak occurs - the resources are freed once the hung process is terminated and the resource usage is constant during the hang. Only the process that is connected to the fake Server is affected. This is an application bug, not a security issue

Why it matters now

EPSS 0.00956 61st percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix No fix listed No fixed version in the sources yet

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
——all versions—No fix listedCNA
  • — Vendor— Affected all versions Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:realvnc:vnc_viewer:6.21.406:*:*:*:*:*:*:*6.21.406VulnerableRealvnc
  • cpe:2.3:a:realvnc:vnc_viewer:6.21.406:*:*:*:*:*:*:* Versions 6.21.406 Vulnerable ·Realvnc

Remediation

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-41380
  2. 2026-10-03 Alias added: GHSA-789c-r6w2-66gw

References

Exploit 1

  • TI-2022-20315 RealVNC VNC Server before 6.11.0 and VNC Viewer before 6.22.826 on Windows allow local… CVSS 3.1HIGH 7.8

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences