Published:
28 March 2001
Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2001.128 -- Microsoft Security Bulletin MS01-017 (version 2.0) Erroneous VeriSign-Issued Digital Certificates Pose Spoofing Hazard 29 March 2001 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Impact: Reduced Security Provide Misleading Information Access Required: Remote Ref: AL-2001.04 - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- - - --------------------------------------------------------------------- - - - Title: Erroneous VeriSign-Issued Digital Certificates Pose Spoofing Hazard Released: 22 March 2001 Revised: 28 March 2001 (version 2.0) Software: All Microsoft operating systems Impact: Attacker could digitally sign code using the name "Microsoft Corporation". Bulletin: MS01-017 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-017.asp. - - --------------------------------------------------------------------- - - - Reason for Revision: ==================== The software update discussed in the original version of the bulletin is now available. Issue: ====== In mid-March 2001, VeriSign, Inc., advised Microsoft that on January 29 and 30, 2001, it issued two VeriSign Class 3 code-signing digital certificates to an individual who fraudulently claimed to be a Microsoft employee. The common name assigned to both certificates is "Microsoft Corporation". The ability to sign executable content using keys that purport to belong to Microsoft would clearly be advantageous to an attacker who wished to convince users to allow the content to run. The certificates could be used to sign programs, ActiveX controls, Office macros, and other executable content. Of these, signed ActiveX controls and Office macros would pose the greatest risk, because the attack scenarios involving them would be the most straightforward. Both ActiveX controls and Word documents can be delivered via either web pages or HTML mails. ActiveX controls can be automatically invoked via script, and Word documents can be automatically opened via script unless the user has applied the Office Document Open Confirmation Tool. Even though the certificates say they are owned by Microsoft, they are not bona fide Microsoft certificates, and content signed by them would not be trusted by default. Trust is defined on a certificate- by-certificate basis, rather than on the basis of the common name. As a result, a warning dialogue would be displayed before any of the signed content could be executed, even if the user had previously agreed to trust other certificates with the common name "Microsoft Corporation". The danger, of course, is that even a security- conscious user might agree to let the content execute, and might agree to always trust the bogus certificates. VeriSign has revoked the certificates, and they are listed in VeriSign's current Certificate Revocation List (CRL). However, because VeriSign's code-signing certificates do not specify a CRL Distribution Point (CDP), it is not possible for any browser's CRL- checking mechanism to locate and use the VeriSign CRL. Microsoft has developed an update that rectifies this problem. The update package includes a CRL containing the two certificates, and an installable revocation handler that consults the CRL on the local machine, rather than attempting to use the CDP mechanism. Customers should take notice of the caveats listed below in the section titled "Additional information about this patch", and in particular should note that the update will need to be re-installed when upgrading to any currently-available version of Windows or Internet Explorer. Versions of Windows beginning with Windows XP Gold and Windows 2000 Service Pack 2, and versions of Internet Explorer beginning with IE 6 will not require the update to be re-installed. Customers who do not wish to install the update should take the following steps to protect themselves in the event that they encounter hostile code signed by one of the certificates: - Visually inspect the certificates cited in all warning dialogues. The two certificates at issue here were issued on 29 and 30 January 2001, respectively. No bona fide Microsoft certificates were issued on these dates. The FAQ and Knowledge Base article Q293817 provide complete details regarding both certificates. - Install the Outlook Email Security Update (http://www.officeupdate.com/2000/downloadDetails/Out2ksec.htm) to prevent mail-borne programs from being launched, even via signed components, and install the Office Document Open Confirmation Tool (http://officeupdate.microsoft.com/downloadDetails/confirm.htm) to force web pages to request permission before opening Office documents. Mitigating Factors: ==================== - The certificates are not trusted by default. As a result, neither programs nor ActiveX controls could be made to run without displaying a warning dialogue. By viewing the certificate in such dialogues, users can easily recognize the certificates. - The certificates are not the bona fide Microsoft code-signing certificates. Content signed by those keys can be distinguished from bona fide Microsoft content. Patch Availability: =================== - A patch is available to fix this vulnerability. Please read Security Bulletin http://www.microsoft.com/technet/security/bulletin/ms01-017.asp for information on obtaining this patch. - - --------------------------------------------------------------------- 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. - -----BEGIN PGP SIGNATURE----- Version: PGP Personal Privacy 6.5.3 iQEVAwUBOsKSq40ZSRQxA/UrAQH1Fgf/cCCX2BadVfwic8mFKOVZy2vMTa+dKxLa aSxO4qUuhZHMj0/uhbSzEZEtlvnnzFisDVhxrrVmUBOR1DbSbX3qHC3SOmCwEjbN Gi1vei7HgCTEKSStTyElCarbGDudVRLQsP7CC0O7dCOQ6gApaRrXqYcLqhJVfwIM O7+yubtDtv+InM7u/eex3gRqHHJJE2jCi+wEAAGqHBT/esvLYkxTM4+4x7mScsHn P+VTACmj0Qc3NK3DwvIVOohpR1k6qIPJijvmoFnAti7yWuld4McUI4IBxHb8NFo1 E7bX7JXyZBrY5sx//o67pFjegISJlY6bD3iMZN0K+MGz/9sTIqjFLA== =765Q - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to use any or all of this information is the responsibility of each user or organisation, and should be done so in accordance with site policies and procedures. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the original authors to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/Information/advisories.html If you believe that your system has been compromised, contact AusCERT or your representative in FIRST (Forum of Incident Response and Security Teams). Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for emergencies. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBOsNHRCh9+71yA2DNAQFYrwQAhWIe2OH9SU/D/E8rjcOgxrJKT9qx2LLj tweBP95DVB9M+H/C+v6c5JDCzS9YO7hnobcgbd+a7+dx3X6kaf1aa2DOm1qqNEy3 2SeKLLW7Q1+enDPV1LMgFW06QdPH0KCGaEgUpROGUtuVLRUj0q7jlVLmc9YQoXYG 7Vv/iRN0llg= =ttZP -----END PGP SIGNATURE-----