Microsoft issues workaround for IE 0 day exploit

On September 17th Microsoft issued an Emergency security advisory with advice on how to patch a Internet Explorer zero-day vulnerability recently spotted being exploited in the wild.

From the Microsoft Website:

“Microsoft Security Advisory (2757760)
Vulnerability in Internet Explorer Could Allow Remote Code Execution
Published: Monday, September 17, 2012
Version: 1.0
General Information
Executive Summary

Microsoft is investigating public reports of a vulnerability in Internet Explorer 6, Internet Explorer 7, Internet Explorer 8, and Internet Explorer 9. Internet Explorer 10 is not affected. Microsoft is aware of targeted attacks that attempt to exploit this vulnerability.

A remote code execution vulnerability exists in the way that Internet Explorer accesses an object that has been deleted or has not been properly allocated. The vulnerability may corrupt memory in a way that could allow an attacker to execute arbitrary code in the context of the current user within Internet Explorer. An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website.

On completion of this investigation, Microsoft will take the appropriate action to protect our customers, which may include providing a solution through our monthly security update release process, or an out-of-cycle security update, depending on customer needs.

We are actively working with partners in our Microsoft Active Protections Program (MAPP) to provide information that they can use to provide broader protections to customers. In addition, we are actively working with partners to monitor the threat landscape and take action against malicious sites that attempt to exploit this vulnerability.

Microsoft continues to encourage customers to follow the guidance in the Microsoft Safety & Security Center of enabling a firewall, applying all software updates and installing anti-virus and anti-spyware software.

Mitigating Factors:

• By default, Internet Explorer on Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability.
• By default, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML email messages in the Restricted sites zone. The Restricted sites zone, which disables script and ActiveX controls, helps reduce the risk of an attacker being able to use this vulnerability to execute malicious code. If a user clicks a link in an email message, the user could still be vulnerable to exploitation of this vulnerability through the web-based attack scenario.
• An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
• In a web-based attack scenario, an attacker could host a website that contains a webpage that is used to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker’s website.

Recommendation. See the Suggested Actions section of this advisory for more information.

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Advisory Details
Affected and Non-Affected Software
This advisory discusses the following software.

Affected Software

Non-Affected Software

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Frequently Asked Questions

What is the scope of the advisory?
Microsoft is aware of a new vulnerability that affects Internet Explorer 6, Internet Explorer 7, Internet Explorer 8, and Internet Explorer 9.

Is this a security vulnerability that requires Microsoft to issue a security update?
On completion of our investigation, Microsoft will take the appropriate action to protect our customers, which may include providing a solution through our monthly security update release process, or an out-of-cycle security update, depending on customer needs.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. If the current user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

How could an attacker exploit the vulnerability?
An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website. The attacker could also take advantage of compromised websites and websites that accept or host user-provided content or advertisements. These websites could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to view the attacker-controlled content. Instead, an attacker would have to convince users to take action, typically by getting them to click a link in an email message or in an Instant Messenger message that takes users to the attacker’s website, or by opening an attachment sent through email.

I am running Internet Explorer for Windows Server 2003, Windows Server 2008, or Windows Server 2008 R2. Does this mitigate this vulnerability?
Yes. By default, Internet Explorer on Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2 runs in a restricted mode that is known as Enhanced Security Configuration. Enhanced Security Configuration is a group of preconfigured settings in Internet Explorer that can reduce the likelihood of a user or administrator downloading and running specially crafted web content on a server. This is a mitigating factor for websites that you have not added to the Internet Explorer Trusted sites zone.

What is the Enhanced Mitigation Experience Toolkit v3.0 (EMET)?
The Enhanced Mitigation Experience Toolkit (EMET) is a utility that helps prevent vulnerabilities in software from being successfully exploited. EMET achieves this by using security mitigation technologies. These technologies function as special protections and obstacles that an exploit author must defeat in order to exploit software vulnerabilities. These security mitigation technologies do not guarantee that vulnerabilities cannot be exploited, but work to make exploitation as difficult to accomplish as possible. In many instances, a fully functional exploit that can bypass EMET may never be developed. For more information, see Microsoft Knowledge Base Article 2458544.

Does EMET help mitigate attacks that try to exploit this vulnerability?
Yes. The Enhanced Mitigation Experience Toolkit (EMET) helps mitigate the exploitation of this vulnerability by adding additional protection layers that make the vulnerability harder to exploit. EMET is a utility that helps prevent vulnerabilities in software from being successfully exploited for code execution, by applying the latest security mitigation technologies. At this time, EMET is provided with limited support and is only available in the English language. For more information, see Microsoft Knowledge Base Article 2458544.

What is Address Space Layout Randomization (ASLR)?
Systems implementing Address Space Layout Randomization (ASLR) relocate normally-predictable function entry points pseudo-randomly in memory. Windows ASLR re-bases system DLLs and executables into one of 256 random locations in memory. Therefore, attackers using hardcoded addresses are likely to “guess correctly” one in 256 times. For more information regarding ASLR, visit the TechNet Magazine article, Inside the Windows Vista Kernel: Part 3.

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Suggested Actions
Apply Workarounds

Workarounds refer to a setting or configuration change that does not correct the underlying issue but would help block known attack vectors before a security update is available. See the next section, Workarounds, for more information.

Workarounds

• Deploy the Enhanced Mitigation Experience Toolkit

Enhanced Mitigation Experience Toolkit (EMET) is a utility that helps prevent vulnerabilities in software from successfully being exploited by applying in-box mitigations such as DEP to applications configured in EMET.

At this time, EMET is provided with limited support and is only available in the English language. For more information, see Microsoft Knowledge Base Article 2458544.

Configure EMET for Internet Explorer from the EMET user interface

To add iexplore.exe to the list of applications using EMET, perform the following steps:

1. Click Start, All Programs, Enhanced Mitigation Experience Toolkit, and EMET 3.0.
2. Click Yes on the UAC prompt, click Configure Apps, then select Add. Browse to the application to be configured in EMET.

   For 32-bit installations of Internet Explorer the location is:
   C:\Program Files (x86)\Internet Explorer\iexplore.exe

   Note For 32-bit systems, the path is c:\program files\Internet Explorer\iexplore.exe

   For 64-bit installations of Internet Explorer the location is:
   C:\Program Files\Internet Explorer\iexplore.exe

3. Click OK and exit EMET.

Configure EMET for Internet Explorer from a command line

• For 32-bit installations of IE on 64-bit systems, run the following from an elevated command prompt:

  “c:\Program Files (x86)\EMET\EMET_Conf.exe”–add “c:\Program Files (x86)\Internet Explorer\iexplore.exe”

  Note For 32-bit systems, the path for EMET is c:\Program Files\EMET\EMET_Conf.exe and the path for IE is c:\Program Files\Internet Explorer\iexplore.exe

• For x64 installations of IE, run the following from an elevated command prompt:

  “c:\Program Files (x86)\EMET\EMET_Conf.exe”–add “c:\Program Files\Internet Explorer\iexplore.exe”

• If you have completed this successfully, the following message displays:

  “The changes you have made may require restarting one or more applications”

• If the application has already been added in EMET, the following message displays:

  Error: “c:\Program Files (x86)\Internet Explorer\iexplore.exe” conflicts with existing entry for “C:\Program Files (x86)\Internet Explorer\iexplore.exe”

• Set Internet and Local intranet security zone settings to “High” to block ActiveX Controls and Active Scripting in these zones

You can help protect against exploitation of this vulnerability by changing your settings for the Internet security zone to block ActiveX controls and Active Scripting. You can do this by setting your browser security to High.

To raise the browsing security level in Internet Explorer, perform the following steps:

1. On the Internet Explorer Tools menu, click Internet Options.
2. In the Internet Options dialog box, click the Security tab, and then click Internet.
3. Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
4. Click Local intranet.
5. Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
6. Click OK to accept the changes and return to Internet Explorer.

Note If no slider is visible, click Default Level, and then move the slider to High.

Note Setting the level to High may cause some websites to work incorrectly. If you have difficulty using a website after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly even with the security setting set to High.

Impact of workaround. There are side effects to blocking ActiveX Controls and Active Scripting. Many websites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use ActiveX Controls to provide menus, ordering forms, or even account statements. Blocking ActiveX Controls or Active Scripting is a global setting that affects all Internet and intranet sites. If you do not want to block ActiveX Controls or Active Scripting for such sites, use the steps outlined in “Add sites that you trust to the Internet Explorer Trusted sites zone”.

Add sites that you trust to the Internet Explorer Trusted sites zone

After you set Internet Explorer to block ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted websites exactly as you do today, while helping to protect yourself from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.

To do this, perform the following steps:

1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.
2. In the Select a web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.
3. If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box.
4. In the Add this website to the zone box, type the URL of a site that you trust, and then click Add.
5. Repeat these steps for each site that you want to add to the zone.
6. Click OK two times to accept the changes and return to Internet Explorer.

Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update.

• Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone

You can help protect against exploitation of this vulnerability by changing your settings to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone. To do this, perform the following steps:

1. In Internet Explorer, click Internet Options on the Tools menu.
2. Click the Security tab.
3. Click Internet, and then click Custom Level.
4. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
5. Click Local intranet, and then click Custom Level.
6. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
7. Click OK two times to return to Internet Explorer.

Note Disabling Active Scripting in the Internet and Local intranet security zones may cause some websites to work incorrectly. If you have difficulty using a website after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly.

Impact of workaround. There are side effects to prompting before running Active Scripting. Many websites that are on the Internet or on an intranet use Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use Active Scripting to provide menus, ordering forms, or even account statements. Prompting before running Active Scripting is a global setting that affects all Internet and intranet sites. You will be prompted frequently when you enable this workaround. For each prompt, if you feel you trust the site that you are visiting, click Yes to run Active Scripting. If you do not want to be prompted for all these sites, use the steps outlined in “Add sites that you trust to the Internet Explorer Trusted sites zone”.

Add sites that you trust to the Internet Explorer Trusted sites zone

After you set Internet Explorer to require a prompt before it runs ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted websites exactly as you do today, while helping to protect you from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.

To do this, perform the following steps:

1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.
2. In the Select a web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.
3. If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box.
4. In the Add this website to the zone box, type the URL of a site that you trust, and then click Add.
5. Repeat these steps for each site that you want to add to the zone.
6. Click OK two times to accept the changes and return to Internet Explorer.

Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update.

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Additional Suggested Actions

• Keep Third-party Software Updated

Current exploits of this vulnerability in Internet Explorer use third-party software, including Oracle’s Java, to help obtain reliable exploitation. Please review Oracle’s guidance regarding Java:

Where can I get the latest version of Java 6?

What is Java Update?

Why should I uninstall older versions of Java from my system?

• Protect your PC

We continue to encourage customers to follow our Protect Your Computer guidance of enabling a firewall, getting software updates and installing antivirus software. For more information, see Microsoft Safety & Security Center.

• Keep Microsoft Software Updated

Users running Microsoft software should apply the latest Microsoft security updates to help make sure that their computers are as protected as possible. If you are not sure whether your software is up to date, visit Microsoft Update, scan your computer for available updates, and install any high-priority updates that are offered to you. If you have automatic updating enabled and configured to provide updates for Microsoft products, the updates are delivered to you when they are released, but you should verify that they are installed.”

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