__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft Certificate Validation Vulnerability [Microsoft Security Bulletin MS02-050] September 5, 2002 21:00 GMT Number M-121 ______________________________________________________________________________ PROBLEM: Flaws in the following products could enable identity spoofing by allowing an attacker to act as a Certificate Authority and to create subordinate certificates. PLATFORM: Microsoft Windows 98 Microsoft Windows 98 Second Edition Microsoft Windows ME Microsoft Windows NT 4.0 Microsoft Windows NT 4.0, Terminal Server Edition Microsoft Windows 2000 Microsoft Windows XP Microsoft Office for Mac Microsoft Internet Explorer for Mac Microsoft Outlook Express for Mac DAMAGE: An attacker could present a false sense of security in the trusted identity of digital certificate senders. SOLUTION: Apply patches as Microsoft releases them for each product. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. In general, man-in-the-middle attacks such ASSESSMENT: as this one are more difficult to exploit. Attackers must successfully convince targeted users of their (attacker's) legitimate certificate through e-mail or web site. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-121.shtml ORIGINAL BULLETIN: http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS02-050.asp PATCHES: Monitor Microsoft's bulletin for patch releases. ______________________________________________________________________________ [***** Start Microsoft Security Bulletin MS02-050 *****] Summary Who should read this bulletin: Customers using Microsoft® Windows®, Office for Mac, Internet Explorer for Mac, or Outlook Express for Mac. Impact of vulnerability: Identity spoofing. Maximum Severity Rating: Critical Recommendation: Administrators should install the patch immediately. Affected Software: Microsoft Windows 98 Microsoft Windows 98 Second Edition Microsoft Windows Me Microsoft Windows NT® 4.0 Microsoft Windows NT 4.0, Terminal Server Edition Microsoft Windows 2000 Microsoft Windows XP Microsoft Office for Mac Microsoft Internet Explorer for Mac Microsoft Outlook Express for Mac Technical details Technical description: The IETF Profile of the X.509 certificate standard defines several optional fields that can be included in a digital certificate. One of these is the Basic Constraints field, which indicates the maximum allowable length of the certificate’s chain and whether the certificate is a Certificate Authority or an end-entity certificate. However, the APIs within CryptoAPI that construct and validate certificate chains (CertGetCertificateChain(), CertVerifyCertificateChainPolicy(), and WinVerifyTrust()) do not check the Basic Constraints field. The same flaw, unrelated to CryptoAPI, is also present in several Microsoft products for Macintosh. The vulnerability could enable an attacker who had a valid end-entity certificate to issue a subordinate certificate that, although bogus, would nevertheless pass validation. Because CryptoAPI is used by a wide range of applications, this could enable a variety of identity spoofing attacks. These are discussed in detail in the FAQ, but could include: Setting up a web site that poses as a different web site, and "proving" its identity by establishing an SSL session as the legitimate web site. Sending emails signed using a digital certificate that purportedly belongs to a different user. Spoofing certificate-based authentication systems to gain entry as a highly privileged user. Digitally signing malware using an Authenticode certificate that claims to have been issued to a company users might trust. Mitigating factors: Overall: The user could always manually check a certificate chain, and might notice in the case of a spoofed chain that there was an unfamiliar intermediate CA. Unless the attacker’s digital certificate were issued by a CA in the user’s trust list, the certificate would generate a warning when validated. The attacker could only spoof certificates of the same type as the one he or she possessed. In the case where the attacker attempted an attack using a high-value certificate such as Authenticode certificates, this would necessitate obtaining a legitimate certificate of the same type – which could require the attacker to prove his or her identity or entitlement to the issuing CA. Web Site Spoofing: The vulnerability provides no way for the attacker to cause the user to visit the attacker’s web site. The attacker would need to redirect the user to a site under the attacker’s control using a method such as DNS poisoning. As discussed in the FAQ, this is extremely difficult to carry out in practice. The vulnerability could not be used to extract information from the user's computer. The vulnerability could only be used by an attacker as a means of convincing a user that he or she has reached a trusted site, in the hope of persuading the user to voluntarily provide sensitive data. Email Signing: The "from" address on the spoofed mail would need to match the one specified in the certificate, giving rise to either of two scenarios if a recipient replied to the mail. In the case where the "from" and "reply-to" fields matched, replies would be sent to victim of the attack rather than the attacker. In the case where the fields didn’t match, replies would obviously be addressed to someone other than ostensible sender. Either case could be a tip-off that an attack was underway. Certificate-based Authentication: In most cases where certificates are used for user authentication, additional information contained within the certificate is necessary to complete the authentication. The type and format of such data typically varies with every installation, and as a result significant insider information would likely be required for a successful attack. Authenticode Spoofing: To the best of Microsoft’s knowledge, such an attack could not be carried out using any commercial CA’s Authenticode certificates. These certificates contain policy information that causes the Basic Constraints field to be correctly evaluated, and none allow end-entity certificates to act as CAs. Even if an attack were successfully carried out using an Authenticode certificate that had been issued by a corporate PKI, it wouldn’t be possible to avoid warning messages, as trust in Authenticode is brokered on a per-certificate, not per-name, basis. Severity Rating: Internet Intranet Client Servers Servers Systems Windows 98 Critical Critical Critical Windows 98 Second Edition Critical Critical Critical Windows Me Critical Critical Critical Windows NT 4.0 Critical Critical Critical Windows NT 4.0, Terminal Server Edition Critical Critical Critical Windows 2000 Professional Critical Critical Critical Windows 2000 Server Critical Critical Critical Windows 2000 Advanced Critical Critical Critical Server Windows XP Critical Critical Critical Microsoft Office for Mac None None Moderate Microsoft Internet Explorer for Mac None None Moderate Microsoft Outlook Express None None Moderate for Mac The above assessment is based on the types of systems affected by the vulnerability, their typical deployment patterns, and the effect that exploiting the vulnerability would have on them. The severity for the Windows products is higher because the vulnerability lies within CryptoAPI and therefore affects many applications and functions. The severity for the Mac products is lower since they use certificates only for SSL. Vulnerability identifier: CAN-2002-0862 Tested Versions: Microsoft tested the following products to assess whether they are affected by this vulnerability. Microsoft Windows 98 Microsoft Windows 98 Second Edition Microsoft Windows Me Microsoft Windows NT 4.0 Microsoft Windows NT 4.0, Terminal Server Edition Microsoft Windows 2000 Microsoft Windows XP Microsoft Office v.X for Mac Microsoft Office 2001 for Mac Microsoft Office 98 for the Macintosh Microsoft Internet Explorer for Mac (for Mac OS 8.1 to 9.x) Microsoft Internet Explorer for Mac (for OS X) Microsoft Outlook Express 5.0.5 for Mac Previous versions are no longer supported, and may or may not be affected by this vulnerability. Patch availability Download locations for this patch Microsoft Windows 98: http://www.microsoft.com/windows98/downloads/contents/WUCritical/q328145/default.asp Windows 98 Second Edition: http://www.microsoft.com/windows98/downloads/contents/WUCritical/q328145/default.asp Windows Me: http://download.microsoft.com/download/WINME/PATCH/25386/WINME/EN-US/328145USAM.EXE Windows NT 4.0: http://www.microsoft.com/ntserver/nts/downloads/critical/q328145/default.asp Windows NT 4.0 Terminal Server Edition: http://www.microsoft.com/ntserver/terminalserver/downloads/critical/q328145/default.asp Windows 2000: To be released shortly Windows XP: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=42562 Windows XP 64 bit Edition: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=42558 Microsoft Office v.X for Mac: To be released shortly Microsoft Office 2001 for Mac: To be released shortly Microsoft Office 98 for the Macintosh: To be released shortly Microsoft Internet Explorer for Mac (for OS 8.1 to 9.x): To be released shortly Microsoft Internet Explorer for Mac (for OS X): To be released shortly Microsoft Outlook Express 5.0.5 for Mac: To be released shortly Additional information about this patch Installation platforms: The patch for Windows NT 4.0 can be installed on systems running Windows NT 4.0 Service Pack 6a. The patch for Windows NT 4.0, Terminal Server Edition, can be installed on systems running Windows NT 4.0, Terminal Server Edition Service Pack 6. The patch for Windows XP can be installed on systems running Windows XP Gold and the forthcoming Windows XP Service Pack 1. Inclusion in future service packs: The fix for this issue will be included in Windows 2000 Service Pack 4 and Windows XP Service Pack 2. Reboot needed: Microsoft Windows NT 4.0: Yes Microsoft Windows NT 4.0, Terminal Server Edition: Yes Microsoft Windows XP: Yes Patch can be uninstalled: Microsoft Windows NT 4.0: Yes Microsoft Windows NT 4.0, Terminal Server Edition: Yes Microsoft Windows XP: Yes Superseded patches: None. Verifying patch installation: Windows NT 4.0: To verify that the patch has been installed on the machine, confirm that the following registry key has been created on the machine: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix\Q328145. To verify the individual files, consult the file manifest in Knowledge Base article Q328145. Windows NT 4.0, Terminal Server Edition: To verify that the patch has been installed on the machine, confirm that the following registry key has been created on the machine: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix\Q328145. To verify the individual files, consult the file manifest in Knowledge Base articleQ328145. Windows XP: To verify that the patch has been installed on the machine, confirm that the following registry key has been created on the machine: HKLM\Software\Microsoft\Updates\Windows XP\SP2\Q328145. To verify the individual files, use the date/time and version information provided in the following registry key: HKLM\Software\Microsoft\Updates\Windows XP\SP2\Q328145\Filelist Caveats: None Localization: Localized versions of this patch are available at the locations discussed in "Patch Availability". Obtaining other security patches: Patches for other security issues are available from the following locations: Security patches are available from the Microsoft Download Center, and can be most easily found by doing a keyword search for "security_patch". Patches for consumer platforms are available from the WindowsUpdate web site Other information: Support: Microsoft Knowledge Base article Q328145 discusses this issue and will be available approximately 24 hours after the release of this bulletin. Knowledge Base articles can be found on the Microsoft Online Support web site. Technical support is available from Microsoft Product Support Services. There is no charge for support calls associated with security patches. Security Resources: The Microsoft TechNet Security Web Site provides additional information about security in Microsoft products. Disclaimer: 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. Revisions: V1.0 (September 04, 2002): Bulletin Created. [***** End Microsoft Security Bulletin MS02-050 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft Corporation for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. 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Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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