-----Original Message-----
From: UNIRAS (UK Govt CERT)
Sent: 19 September 2002 09:54
To: [EMAIL PROTECTED]
Subject: UNIRAS Brief - 323/02 - Microsoft - Cryptographic Flaw in RDP
Protocol can Lead to Information Disclosure
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UNIRAS (UK Govt CERT) Briefing Notice - 323/02 dated 19.08.02 Time: 09:40
UNIRAS is part of NISCC(National Infrastructure Security Co-ordination Centre)
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UNIRAS material is also available from its website at www.uniras.gov.uk and
Information about NISCC is available from www.niscc.gov.uk
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Title
=====
Microsoft Security Bulletin - MS02-051:
Cryptographic Flaw in RDP Protocol can Lead to Information Disclosure
Detail
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Title: Cryptographic Flaw in RDP Protocol can Lead to
Information Disclosure (Q324380)
Released: 18 September 2002
Software: Microsoft Windows 2000
Microsoft Windows XP
Impact: Two vulnerabilities: information disclosure, denial of
service
Max Risk: Moderate
Bulletin: MS02-051
Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-051.asp.
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Issue:
======
The Remote Data Protocol (RDP) provides the means by which Windows
systems can provide remote terminal sessions to clients. The protocol
transmits information regarding a terminal sessions' keyboard, mouse
and video to the remote client, and is used by Terminal Services in
Windows NT 4.0 and Windows 2000, and by Remote Desktop in Windows XP.
Two security vulnerabilities, both of which are eliminated by this
patch, have been discovered in various RDP implementations.
The first involves how session encryption is implemented in certain
versions of RDP. All RDP implementations allow the data in an RDP
session to be encrypted. However, in the versions in Windows 2000 and
Windows XP, the checksums of the plaintext session data are sent
without being encrypted themselves. An attacker who was able to
eavesdrop on and record an RDP session could conduct a straight-
forward cryptanalytic attack against the checksums and recover
the session traffic.
The second involves how the RDP implementation in Windows XP handles
data packets that are malformed in a particular way. Upon receiving
such packets, the Remote Desktop service would fail, and with it
would fail the operating system. It would not be necessary for an
attacker to authenticate to an affected system in order to deliver
packets of this type to an affected system.
Mitigating Factors:
====================
Cryptographic Flaw in RDP Protocol:
- - - An attacker would need the ability to capture an RDP session in
order to exploit this vulnerability. In most cases, this would re-
quire that the attacker have physical access to the network media.
- - - Because encryption keys are negotiated on a per-session basis, a
successful attack would allow an attacker to decrypt only a single
session and not multiple sessions. Thus, the attacker would need to
conduct a separate cryptanalytic attack against each session he or
she wished to compromise.
Denial of Service in Remote Desktop:
- - - Remote Desktop service in Windows XP is not enabled by default.
- - - Even if Remote Desktop service were enabled, a successful attack
would require that the attacker be able to deliver packets to the
Remote Desktop port on an affected system. Customers who block port
3389 at the firewall would be protected against attempts to exploit
this vulnerability. (By default Internet Connection Firewall does
block port 3389).
Maximum Risk Rating:
====================
- Internet systems: Moderate
- Intranet systems: Moderate
- Client systems: Moderate
Patch Availability:
===================
- A patch is available to fix this vulnerability. Please read the
Security Bulletin at
http://www.microsoft.com/technet/security/bulletin/ms02-051.asp
for information on obtaining this patch.
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THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY
DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN
IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.
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*******************************************************************
Reprinted with permission of Microsoft Corporation.
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For additional information or assistance, please contact the HELP Desk by
telephone or Not Protectively Marked information may be sent via EMail to:
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Tel: 020 7821 1330 Ext 4511
Fax: 020 7821 1686
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UNIRAS wishes to acknowledge the contributions of Microsoft for the information
contained in this Briefing.
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This Briefing contains the information released by the original author. Some
of the information may have changed since it was released. If the vulnerability
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and has contacts with other international Incident Response Teams (IRTs) in
order to foster cooperation and coordination in incident prevention, to prompt
rapid reaction to incidents, and to promote information sharing amongst its
members and the community at large.
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<End of UNIRAS Briefing>
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