#2014-007 libvncserver multiple issues

Description:

Virtual Network Computing (VNC) is a graphical sharing system based on the
Remote Frame Buffer (RFB) protocol.

The LibVNCServer project, an open source library for implementing VNC
compliant communication, suffers from a number of bugs that can be potentially
exploited with security impact.

Various implementation issues resulting in remote code execution and/or DoS
conditions on both the VNC server and client side have been discovered.

 1. A malicious VNC server can trigger incorrect memory management
    handling by advertising a large screen size parameter to the VNC
    client. This would result in multiple memory corruptions and could
    allow remote code execution on the VNC client.

 2. A malicious VNC client can trigger multiple DoS conditions on the VNC
    server by advertising a large screen size, ClientCutText message
    length and/or a zero scaling factor parameter.

 3. A malicious VNC client can trigger multiple stack-based buffer
    overflows by passing a long file and directory names and/or attributes
    (FileTime) when using the file transfer message feature.

It should be noted that every described issue represents a post-authentication
bug, therefore the server side conditions can be anonymously leveraged only if
the VNC server is configured to allow unauthenticated sessions.

Affected version:

LibVNCServer <= 0.9.9

Fixed version:

LibVNCServer, N/A

Credit: vulnerability report received from Nicolas Ruff
        of Google Security Team <nruff AT google.com>.

CVE: CVE-2014-6051 (1), CVE-2014-6052 (1), CVE-2014-6053 (2),
     CVE-2014-6054 (2), CVE-2014-6055 (3)

Timeline:

2014-09-05: vulnerability report received
2014-09-16: contacted affected vendors
2014-09-22: contacted additional affected vendors
2014-09-25: advisory release

References:
(1) https://github.com/newsoft/libvncserver/commit/045a044e8ae79db9244593fbce154cdf6e843273
(2) https://github.com/newsoft/libvncserver/commit/6037a9074d52b1963c97cb28ea1096c7c14cbf28
(2) https://github.com/newsoft/libvncserver/commit/05a9bd41a8ec0a9d580a8f420f41718bdd235446
(3) https://github.com/newsoft/libvncserver/commit/06ccdf016154fde8eccb5355613ba04c59127b2e
(3) https://github.com/newsoft/libvncserver/commit/f528072216dec01cee7ca35d94e171a3b909e677

Permalink:
https://www.ocert.org/advisories/ocert-2014-007.html

-- 
Andrea Barisani |                Founder & Project Coordinator
          oCERT | OSS Computer Security Incident Response Team

<lcars@ocert.org>                         https://www.ocert.org
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