Vulnerability in Workstation Service Allows Code Execution (MS06-070)
15 Nov. 2006
Summary
A remote code execution vulnerability exists in the Workstation service that could allow an attacker who successfully exploited this vulnerability to take complete control of the affected system.
Non-Affected Software:
* Microsoft Windows XP Professional x64 Edition
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1
* Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems
* Microsoft Windows Server 2003 x64 Edition
* Windows Vista
Mitigating Factors for Workstation Service Memory Corruption Vulnerability - CVE-2006-4691:
* Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed.
* For Windows Server 2003 the affected component is not vulnerable.
* On Windows XP Service Pack 2 the attack could only be successfully performed by a user with Administrator privileges.
Workarounds for Workstation Service Memory Corruption Vulnerability - CVE-2006-4691:
Microsoft has tested the following workarounds. Although these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.
* Block TCP ports 139 and 445 at the firewall:
These ports are used to initiate a connection with the affected component. Blocking TCP ports 139 and 445 at the firewall will help protect systems that are behind that firewall from attempts to exploit this vulnerability. We recommend that you block all unsolicited inbound communication from the Internet to help prevent attacks that may use other ports. For more information about ports, visit the following Web site.
Impact of Workaround: Several Windows services use the affected ports. Blocking connectivity to the ports may cause various applications or services to not function. Some of the applications or services that could be impacted are listed below.
Applications that uses SMB (CIFS)
Applications that uses mailslots or named pipes (RPC over SMB)
Server (File and Print Sharing)
Group Policy
Net Logon
Distributed File System (DFS)
Terminal Server Licensing
Print Spooler
Computer Browser
Remote Procedure Call Locator
Fax Service
Indexing Service
Performance Logs and Alerts
Systems Management Server
License Logging Service
* To help protect from network-based attempts to exploit this vulnerability, use a personal firewall, such as the Windows Firewall, which is included with Windows XP.
By default, the Windows Firewall feature in Windows XP helps protect your Internet connection by blocking unsolicited incoming traffic. We recommend that you block all unsolicited incoming communication from the Internet.
To enable the Windows Firewall feature by using the Network Setup Wizard, follow these steps:
1. Click Start, and then click Control Panel.
2. Double-click Network Connections and then click Change Windows Firewall settings.
3. On the General tab, ensure that the On (recommended) value is selected. This will enable the Windows Firewall.
4. Once the Windows Firewall is enabled, select Don t allow exceptions to prohibit all incoming traffic.
* If you want to enable certain programs and services to communicate through the firewall, de-select Don t allow exceptions and click the Exceptions tab. On the Exception tab, select the programs, protocols, and services you want to enable.
* To help protect from network-based attempts to exploit this vulnerability, enable advanced TCP/IP filtering on systems that support this feature.
You can enable advanced TCP/IP filtering to block all unsolicited inbound traffic. For more information about how to configure TCP/IP filtering, see Microsoft Knowledge Base Article 309798.
* To help protect from network-based attempts to exploit this vulnerability, block the affected ports by using IPSec on the affected systems.
Use Internet Protocol security (IPSec) to help protect network communications. Detailed information about IPSec and about how to apply filters is available in Microsoft Knowledge Base Article 313190 and Microsoft Knowledge Base Article 813878.
FAQ for Workstation Service Memory Corruption Vulnerability - CVE-2006-4691: What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could remotely 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.
What causes the vulnerability?
An unchecked buffer in the Workstation service.
What is the Workstation service?
Both local file system requests and remote file or print network requests are routed through the Workstation service. This service determines where the resource is located and then routes the request to the local file system or to the networking components. When the Workstation service is stopped, all requests are assumed to be local requests.
What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of the affected system.
Who could exploit the vulnerability?
On Windows 2000 Service Pack 4 any anonymous user who could deliver a specially crafted message to the affected system could try to exploit this vulnerability. On Windows XP Service Pack 2 the attack could only be successfully performed by a user with Administrator privileges.
How could an attacker exploit the vulnerability?
An attacker could try to exploit the vulnerability by creating a specially crafted message and sending the message to an affected system. The message could then cause the affected system to execute code.
What systems are primarily at risk from the vulnerability?
Systems running Windows 2000 Service Pack 4 and Windows XP Service Pack 2 are primarily at risk from this vulnerability.
Could the vulnerability be exploited over the Internet?
Yes. An attacker could try to exploit this vulnerability over the Internet. Firewall best practices and standard default firewall configurations can help protect against attacks that originate from the Internet. Microsoft has provided information about how you can help protect your PC. End users can visit the Protect Your PC Web site. IT professionals can visit the Security Guidance Center Web site.
What does the update do?
The update removes the vulnerability by modifying the way that the Workstation service validates the length of a message before it passes the message to the allocated buffer.
When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.
When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.
