RealVNC Remote Authentication Bypass Vulnerability



Date Discovered

May 15, 2006


RealVNC is susceptible to an authentication-bypass vulnerability. This issue is due to a flaw in the authentication process of the affected package. Exploiting this issue allows attackers to gain unauthenticated, remote access to the VNC servers. RealVNC 4.1.1 is vulnerable to this issue; other versions may also be affected. UPDATE (May 25, 2006): Reports indicate that this issue is being actively exploited in the wild.

Technologies Affected

  • Cisco IP/VC 3540/DCS
  • RealVNC RealVNC Enterprise Edition 4.0
  • RealVNC RealVNC Enterprise Edition 4.1
  • RealVNC RealVNC Enterprise Edition 4.2
  • RealVNC RealVNC Enterprise Edition 4.2.2
  • RealVNC RealVNC Free Edition 4.0
  • RealVNC RealVNC Free Edition 4.1
  • RealVNC RealVNC Free Edition 4.1.1
  • RealVNC RealVNC Personal Edition 4.0
  • RealVNC RealVNC Personal Edition 4.1
  • RealVNC RealVNC Personal Edition 4.2
  • RealVNC RealVNC Personal Edition 4.2.2


Block external access at the network boundary, unless external parties require service.
If applicable, block access to the computer at the network perimeter. Allow only trusted computers and networks access to resources.

Communicate sensitive information over encrypted channels.
Ensure that access to affected VNC servers occurs only through strongly authenticated means such as VPNs. This will enforce that an extra level of authentication is required to access affected servers.

The vendor has released fixes to address this issue.



Steve Wiseman discovered this vulnerability.

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