The CSecurityTLS::processMsg function in common/rfb/CSecurityTLS.cxx in the vncviewer component in TigerVNC 1.1beta1 does not properly verify the server's X.509 certificate, which allows man-in-the-middle attackers to spoof a TLS VNC server via an arbitrary certificate.

From Red Hat Security Advisory 2011:0871 :

Updated tigervnc packages that fix one security issue are now available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having moderate security impact. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available from the CVE link in the References section.

Virtual Network Computing (VNC) is a remote display system which allows you to view a computer's desktop environment not only on the machine where it is running, but from anywhere on the Internet and from a wide variety of machine architectures. TigerVNC is a suite of VNC servers and clients.

It was discovered that vncviewer could prompt for and send authentication credentials to a remote server without first properly validating the server's X.509 certificate. As vncviewer did not indicate that the certificate was bad or missing, a man-in-the-middle attacker could use this flaw to trick a vncviewer client into connecting to a spoofed VNC server, allowing the attacker to obtain the client's credentials. (CVE-2011-1775)

All tigervnc users should upgrade to these updated packages, which contain a backported patch to correct this issue.

Virtual Network Computing (VNC) is a remote display system which allows you to view a computer's desktop environment not only on the machine where it is running, but from anywhere on the Internet and from a wide variety of machine architectures. TigerVNC is a suite of VNC servers and clients.

It was discovered that vncviewer could prompt for and send authentication credentials to a remote server without first properly validating the server's X.509 certificate. As vncviewer did not indicate that the certificate was bad or missing, a man-in-the-middle attacker could use this flaw to trick a vncviewer client into connecting to a spoofed VNC server, allowing the attacker to obtain the client's credentials. (CVE-2011-1775)

All tigervnc users should upgrade to these updated packages, which contain a backported patch to correct this issue.

The remote Redhat Enterprise Linux 6 host has packages installed that are affected by a vulnerability as referenced in the RHSA-2011:0871 advisory.

    Virtual Network Computing (VNC) is a remote display system which allows you     to view a computer's desktop environment not only on the machine where it     is running, but from anywhere on the Internet and from a wide variety of     machine architectures. TigerVNC is a suite of VNC servers and clients.

    It was discovered that vncviewer could prompt for and send authentication     credentials to a remote server without first properly validating the     server's X.509 certificate. As vncviewer did not indicate that the     certificate was bad or missing, a man-in-the-middle attacker could use this     flaw to trick a vncviewer client into connecting to a spoofed VNC server,     allowing the attacker to obtain the client's credentials. (CVE-2011-1775)

    All tigervnc users should upgrade to these updated packages, which contain     a backported patch to correct this issue.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

This update fixes following issue :

  - vncviewer could have sent user password to VNC server     without proper validation of the server's X.509     certificate when secure X.509 authentication was     requested (CVE-2011-1775)

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

ID	Name	Product	Family	Severity
68292	Oracle Linux 6 : tigervnc (ELSA-2011-0871)	Nessus	Oracle Linux Local Security Checks	medium
61069	Scientific Linux Security Update : tigervnc on SL6.x i386/x86_64	Nessus	Scientific Linux Local Security Checks	medium
55160	RHEL 6 : tigervnc (RHSA-2011:0871)	Nessus	Red Hat Local Security Checks	medium
54633	Fedora 15 : tigervnc-1.0.90-4.fc15 (2011-6838)	Nessus	Fedora Local Security Checks	medium

Detections

Analytics

CVE-2011-1775

medium

Tenable Plugins

medium

medium

medium

medium