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Article ID: 299472 - Last Review: January 31, 2007 - Revision: 5.1

Internet Explorer Vulnerability Affects the Way Digital Certificates from Web Servers Are Validated

Retired KB Content Disclaimer

View products that this article applies to.

This article was previously published under Q299472

SYMPTOMS

A vulnerability exists in Internet Explorer 5.01 and 5.5 that may prevent the following checks from being performed if Certificate Revocation List (CRL) checking for digital certificates provided by Web servers is enabled:

Verification that the certificate has not expired
Verification that the server name matches the name on the certificate
Verification that the issuer of the certificate is trusted

This could potentially enable an attacker's Web site to masquerade as a trusted site.

Mitigating factors:

The vulnerability only affects how certificates from Web servers are validated. It does not affect how code-signing certificates or any other types of certificates are validated.
The specific checks that might be bypassed vary with both the user and the actions that he or she may have taken during the current browsing session. An attacker could not predict with any degree of certainty which checks might be bypassed in a particular case.
The vulnerability does not provide any way to force users to the attacker's Web site. It is likely that this vulnerability could only be exploited in conjunction with a successful "DNS poisoning" or similar attack.

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CAUSE

A flaw in Internet Explorer causes certain certificate checks not to be made when CRL checking has been enabled for server certificates. Specifically, if CRL checking is selected, Internet Explorer may not correctly verify the trust status of the root Certificate Authority (CA), the expiration date for the certificate, or the common name that is specified in the certificate.

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RESOLUTION

For additional information about what is fixed by this patch, click the article number below to view the article in the Microsoft Knowledge Base:

295106 (http://support.microsoft.com/kb/295106/EN-US/ ) Internet Explorer 5.01 and 5.5 Security Rollup Is Available

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Internet Explorer 5.5

To resolve this problem, obtain the latest service pack for Internet Explorer version 5.5. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

267954 (http://support.microsoft.com/kb/267954/EN-US/ ) How to Obtain the Latest Internet Explorer 5.5 Service Pack

For your convenience, the individual update is also available:

The following file is available for download from the Microsoft Download Center:

Collapse this imageExpand this image

Download Q299618.exe now (http://www.microsoft.com/windows/ie/downloads/critical/q299618/default.asp)

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 (http://support.microsoft.com/kb/119591/EN-US/ ) How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English version of this fix should have the following file attributes or later:

   Date        Time    Version         Size       File name  
   ----------------------------------------------------------
   04/02/2001  05:28p  5.50.4616.200   2,748,688  Mshtml.dll
   02/20/2001  05:36p  5.50.4614.2000  1,147,152  Shdocvw.dll
   04/02/2001  05:28p  5.50.4616.200     480,528  Wininet.dll

NOTE: This patch requires Internet Explorer 5.5 Service Pack 1.

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Internet Explorer 5.01

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that you determine are at risk of attack. Evaluate your computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your computer. See the associated Microsoft Security Bulletin (http://www.microsoft.com/technet/security/bulletin/MS01-027.mspx) to help determine the degree of risk. This fix may receive additional testing. If your computer is sufficiently at risk, Microsoft recommends that you apply this fix now. Otherwise, wait for the next Internet Explorer 5.01 service pack that contains this fix.

To resolve this problem immediately, download the fix by following the instructions later in this article or contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS (http://support.microsoft.com/default.aspx?scid=fh;en-us;cntactms)

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The following file is available for download from the Microsoft Download Center:

Collapse this imageExpand this image

Download Q295106.exe now (http://www.microsoft.com/windows/ie/download/critical/q295106/default.asp)

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 (http://support.microsoft.com/kb/119591/EN-US/ ) How to Obtain Microsoft Support Files from Online Services

   Date        Time    Version       Size     File name
   ------------------------------------------------------
   04/02/2001  06:55p  5.0.3404.200  461,584  Wininet.dll

NOTE: This patch requires Internet Explorer 5.01 Service Pack 2.

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STATUS

Internet Explorer 5.5

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Internet Explorer 5.5. This problem was first corrected in Internet Explorer version 5.5 Service Pack 2.

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Internet Explorer 5.01

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Internet Explorer 5.01 and Internet Explorer 5.01 Service Packs 1 and 2.

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MORE INFORMATION

For more information about this vulnerability, see the following Microsoft Web site:

http://www.microsoft.com/technet/security/bulletin/MS01-027.mspx (http://www.microsoft.com/technet/security/bulletin/MS01-027.mspx)

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APPLIES TO

Microsoft Internet Explorer 5.5 Service Pack 1
Microsoft Internet Explorer 5.01
Microsoft Internet Explorer 5.5

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kbbug kbfix kbgraphxlinkcritical kbie550presp2fix KB299472

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Retired KB Content Disclaimer

This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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