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National Cyber Alert System
Technical Cyber Security Alert TA12-156A
Microsoft Windows Unauthorized Digital Certificates
Original release date: June 04, 2012
Last revised: --
Source: US-CERT
Systems Affected
All supported versions of Microsoft Windows, including:
* Windows XP and Server 2003
* Windows Vista and Server 2008
* Windows 7 and Server 2008 R2
* Windows 8 Consumer Preview
* Windows Mobile and Phone
Overview
X.509 digital certificates issued by the Microsoft Terminal
Services licensing certificate authority (CA) can be illegitimately
used to sign code. This problem was discovered in the Flame
malware. Microsoft has released updates to revoke trust in the
affected certificates.
Description
Microsoft Security Advisory (2718704) warns of active attacks using
illegitimate certificates issued by the the Microsoft Terminal
Services licensing certificate authority (CA). There appear to be
problems with some combination of weak cryptography and certificate
usage configuration. From an MSRC blog post:
We identified that an older cryptography algorithm could be
exploited and then be used to sign code as if it originated from
Microsoft. Specifically, our Terminal Server Licensing Service,
which allowed customers to authorize Remote Desktop services in
their enterprise, used that older algorithm and provided
certificates with the ability to sign code, thus permitting code
to be signed as if it came from Microsoft.
From another MSRC blog post:
What we found is that certificates issued by our Terminal
Services licensing certification authority, which are intended
to only be used for license server verification, could also be
used to sign code as Microsoft. Specifically, when an enterprise
customer requests a Terminal Services activation license, the
certificate issued by Microsoft in response to the request
allows code signing without accessing Microsofts internal PKI
infrastructure.
The following details about the affected certificates were provided
in Microsoft Security Advisory (2718704):
Certificate: Microsoft Enforced Licensing Intermediate PCA
Issued by: Microsoft Root Authority
Thumbprint: 2a 83 e9 02 05 91 a5 5f c6 dd ad 3f b1 02 79 4c \
52 b2 4e 70
Certificate: Microsoft Enforced Licensing Intermediate PCA
Issued by: Microsoft Root Authority
Thumbprint: 3a 85 00 44 d8 a1 95 cd 40 1a 68 0c 01 2c b0 a3 \
b5 f8 dc 08
Certificate: Microsoft Enforced Licensing Registration Authority
CA (SHA1)
Issued by: Microsoft Root Certificate Authority
Thumbprint: fa 66 60 a9 4a b4 5f 6a 88 c0 d7 87 4d 89 a8 63 \
d7 4d ee 97
Impact
An attacker could obtain a certificate that could be used to
illegitimately sign code as Microsoft. The signed code could then
be used in a variety of attacks in which the code would appear to
be trusted by Windows.
An attacker could offer software that appeared to be signed by a
valid and trusted Microsoft certificate chain. As noted in an MSRC
blog post, "...some components of the [Flame] malware have been
signed by certificates that allow software to appear as if it was
produced by Microsoft."
Solution
It is important to act quickly to revoke trust in the affected
certificates. Any certificates issued by the Microsoft Terminal
Services licensing certificate authority (CA) could be used for
illegitimate purposes and should not be trusted.
Apply updates
Apply the appropriate versions of KB2718704 to add the affected
certificates to the Untrusted Certificate Store. Updates will
reach most users via automatic updates and Windows Server Update
Services (WSUS).
Revoke trust in affected certificates
Manually add the affected certificates to the Untrusted
Certificate Store. The Certifcates MMC snap-in and Certutil
command can be used on Windows systems.
References
* US-CERT Current Activity: Unauthorized Microsoft Digital
Certificates -
<https://www.us-cert.gov/current/#microsoft_unauthorized_digital_certificates>
* Microsoft Security Advisory (2718704) -
<https://technet.microsoft.com/en-us/security/advisory/2718704>
* Unauthorized digital certificates could allow spoofing -
<http://support.microsoft.com/kb/2718704>
* Microsoft certification authority signing certificates added to the
Untrusted Certificate Store -
<https://blogs.technet.com/b/srd/archive/2012/06/03/microsoft-certification-authority-signing-certificates-added-to-the-untrusted-certificate-store.aspx>
* Microsoft releases Security Advisory 2718704 -
<https://blogs.technet.com/b/msrc/archive/2012/06/03/microsoft-releases-security-advisory-2718704.aspx>
* Windows Server Update Services -
<http://technet.microsoft.com/en-us/windowsserver/bb332157.aspx>
* Certutil -
<http://technet.microsoft.com/en-us/library/cc732443%28v=ws.10%29.aspx>
* How to: View Certificates with the MMC Snap-in -
<http://msdn.microsoft.com/en-us/library/ms788967.aspx>
Revision History
June 04, 2012: Initial release
____________________________________________________________________
Feedback can be directed to US-CERT Technical Staff. Please send
email to <cert@xxxxxxxx> with "TA12-156A Feedback INFO#461124" in
the subject.
____________________________________________________________________
Produced by US-CERT, a government organization.
____________________________________________________________________
This product is provided subject to the Notification as indicated here:
http://www.us-cert.gov/legal.html#notify
This document can also be found at
http://www.us-cert.gov/cas/techalerts/TA12-156A.html
For instructions on subscribing to or unsubscribing from this
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