A new update is available for Red Hat Enterprise Linux. Here the announcement:
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Red Hat Security Advisory

Synopsis: Moderate: rdesktop security update
Advisory ID: RHSA-2008:0575-01
Product: Red Hat Enterprise Linux
Advisory URL: https://rhn.redhat.com/errata/RHSA-2008-0575.html
Issue date: 2008-07-24
CVE Names: CVE-2008-1801 CVE-2008-1803
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1. Summary:

An updated rdesktop package that fixes a security issue is now available for
Red Hat Enterprise Linux 5.

This update has been rated as having moderate security impact by the Red
Hat Security Response Team.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Desktop (v. 5 client) - i386, x86_64
Red Hat Enterprise Linux (v. 5 server) - i386, ia64, ppc, s390x, x86_64

3. Description:

rdesktop is an open source client for Microsoft Windows NT Terminal Server
and Microsoft Windows 2000 and 2003 Terminal Services, capable of natively
using the Remote Desktop Protocol (RDP) to present the user's NT desktop.
No additional server extensions are required.

An integer underflow and integer signedness issue were discovered in the
rdesktop. If an attacker could convince a victim to connect to a malicious
RDP server, the attacker could cause the victim's rdesktop to crash or,
possibly, execute an arbitrary code. (CVE-2008-1801, CVE-2008-1803)

Users of rdesktop should upgrade to these updated packages, which contain a
backported patches to resolve these issues.

4. Solution:

Before applying this update, make sure that all previously-released
errata relevant to your system have been applied.

This update is available via Red Hat Network. Details on how to use
the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/FAQ_58_10188

5. Bugs fixed (http://bugzilla.redhat.com/):

445825 - CVE-2008-1801 rdesktop: iso_recv_msg() Integer Underflow Vulnerability
445829 - CVE-2008-1803 rdesktop: channel_process() Integer Signedness Vulnerability

6. Package List:

Red Hat Enterprise Linux Desktop (v. 5 client):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/5Client/en/os/SRPMS/rdesktop-1.4.1-6.src.rpm

i386:
rdesktop-1.4.1-6.i386.rpm
rdesktop-debuginfo-1.4.1-6.i386.rpm

x86_64:
rdesktop-1.4.1-6.x86_64.rpm
rdesktop-debuginfo-1.4.1-6.x86_64.rpm

Red Hat Enterprise Linux (v. 5 server):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/5Server/en/os/SRPMS/rdesktop-1.4.1-6.src.rpm

i386:
rdesktop-1.4.1-6.i386.rpm
rdesktop-debuginfo-1.4.1-6.i386.rpm

ia64:
rdesktop-1.4.1-6.ia64.rpm
rdesktop-debuginfo-1.4.1-6.ia64.rpm

ppc:
rdesktop-1.4.1-6.ppc.rpm
rdesktop-debuginfo-1.4.1-6.ppc.rpm

s390x:
rdesktop-1.4.1-6.s390x.rpm
rdesktop-debuginfo-1.4.1-6.s390x.rpm

x86_64:
rdesktop-1.4.1-6.x86_64.rpm
rdesktop-debuginfo-1.4.1-6.x86_64.rpm

These packages are GPG signed by Red Hat for security. Our key and
details on how to verify the signature are available from
https://www.redhat.com/security/team/key/#package

7. References:

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-1801
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-1803
http://www.redhat.com/security/updates/classification/#moderate

8. Contact:

The Red Hat security contact is . More contact
details at https://www.redhat.com/security/team/contact/

Copyright 2008 Red Hat, Inc.
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RHSA-2008:0576-01 Moderate: rdesktop security update
Apple ships massive Mac OS X 10.4 security upgrade