US-CERT Alert TA12-156A -- Microsoft Windows Unauthorized Digital Certificates

2012-06-06T00:00:00
ID SECURITYVULNS:DOC:28126
Type securityvulns
Reporter Securityvulns
Modified 2012-06-06T00:00:00

Description

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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@cert.org> with "TA12-156A Feedback INFO#461124" in the subject.


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