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Home » Hacking News » Conectiva CLA-2003:640: VNC multiple vulnerabilities

Conectiva CLA-2003:640: VNC multiple vulnerabilities

by Nikola Strahija on May 9th, 2003 Several vulnerabilities have been found in the remote control package, VNC, which, if exploited could allow authorization bypass and thus lead to privilege escalation.


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CONECTIVA LINUX SECURITY ANNOUNCEMENT
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PACKAGE : vnc
SUMMARY : Vulnerabilties in cookies and random challenge generations
DATE : 2003-05-05 17:49:00
ID : CLA-2003:640
RELEVANT
RELEASES : 7.0, 8

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DESCRIPTION
Virtual Network Computing (VNC) is a tool that provides remote
display viewing/controlling.

This update fixes two vulnerabilities found in VNC that affect the
versions distributed with Conectiva Linux 7.0 and 8:

- Weak challenge number generation[1]
VNC uses a challenge-response schema for authentication, but it uses
the same challenge for multiple connections that are done in an
interval of one second. An attacker can exploit this vulnerability by
sniffing the connection and using the same challenge/response of a
valid conection to gain access without having a valid account in the
vnc server. This vulnerability was fixed in TightVNC 1.2.6.

The Common Vulnerabilities and Exposures (CVE) project has assigned
the name CAN-2002-1336 to this issue[2].

- Weak Xcookie generation
When the VNC server acts as an XServer, it generates a
MIT-MAGIC-COOKIE[4] to authenticate users. VNC versions up to
3.3.3r2-21 generate such a cookie in an unsafe manner (not randomly
enough), allowing attackers to more easily guess it. A remote
attacker can access the vnc server without having permission to do so
if it knows the cookie value.

The Common Vulnerabilities and Exposures (CVE) project has assigned
the name CAN-2002-1511 to this issue[3].


SOLUTION
All vnc users should upgrade.


REFERENCES:
1.http://marc.theaimsgroup.com/?l=bugtraq&m=102753170201524
2.http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-1336
3.http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-1511
4.http://www-ugrad.cs.colorado.edu/udp/xauth.html


UPDATED PACKAGES
ftp://atualizacoes.conectiva.com.br/7.0/RPMS/vnc-3.3.3-6U70_2cl.i386.rpm
ftp://atualizacoes.conectiva.com.br/7.0/SRPMS/vnc-3.3.3-6U70_2cl.src.rp
ftp://atualizacoes.conectiva.com.br/8/RPMS/vnc-3.3.3r2+tight1.2.2-6U80_1cl.i386.rpm
ftp://atualizacoes.conectiva.com.br/8/RPMS/vnc-java-3.3.3r2+tight1.2.2-6U80_1cl.i386.rpm
ftp://atualizacoes.conectiva.com.br/8/RPMS/vnc-server-3.3.3r2+tight1.2.2-6U80_1cl.i386.rpm
ftp://atualizacoes.conectiva.com.br/8/SRPMS/vnc-3.3.3r2+tight1.2.2-6U80_1cl.src.rpm


ADDITIONAL INSTRUCTIONS
The apt tool can be used to perform RPM packages upgrades:

- run: apt-get update
- after that, execute: apt-get upgrade

Detailed instructions reagarding the use of apt and upgrade examples
can be found at http://distro.conectiva.com.br/atualizacoes/#apt?idioma=en

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All packages are signed with Conectiva's GPG key. The key and instructions
on how to import it can be found at
http://distro.conectiva.com.br/seguranca/chave/?idioma=en
Instructions on how to check the signatures of the RPM packages can be
found at http://distro.conectiva.com.br/seguranca/politica/?idioma=en

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All our advisories and generic update instructions can be viewed at
http://distro.conectiva.com.br/atualizacoes/?idioma=en

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Copyright (c) 2003 Conectiva Inc.
http://www.conectiva.com

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subscribe: [email protected]
unsubscribe: [email protected]
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